Experiences during developmental periods in early childhood sculpt neural connections, building brain architecture and competencies that impact life-long wellbeing and health trajectories [1]. Young children’s outdoor play is linked to positive health outcomes, and exposure to nature is associated with mental wellbeing, cognitive and social development, and fewer behavioral problems [2–5]. Children are intrinsically motivated to play, spontaneously engaging in joy-inducing activities that build physical, cognitive, social, and emotional skills [6, 7]. Though strongly associated with physical activity (PA), much of the developmental value that children receive from play derives from its intrinsic “unpredictability, spontaneity, goal-lessness and personal control, rather than directly from its content” [8]. Through play, children simulate and overcome hypothetical challenges, enhancing adaptive capabilities, resilience, and self-regulation [9, 10]. Free play permits both problem finding and problem solving; cultivating creativity and unstructured time has been associated with higher executive function [11, 12]. Importantly, play is central to children’s own conception of wellbeing [13]. Despite these benefits, children’s need to play is often overlooked and adult activity patterns prioritized in neighborhood design [14]. With fewer opportunities to experience other environments, children living in poverty may be most impacted by un-playable neighborhoods [15, 16]. In a rapidly urbanizing world, it is critical to understand how built environments shape early childhood exposures, experiences, and behaviors, including outdoor free play (OFP).

Previous work on urban environments and child movement behaviors, including OFP, has often focused on middle childhood and youth, as parental supervision decreases and independent mobility increases [17]. Several recent reviews examined correlates of outdoor play, time, or physical activity [18–21], considering broader age ranges [18–20], older ages [21], or exclusively qualitative [18] or quantitative evidence [19, 20, 22]. Lambert et al. [19] found moderate evidence that lower traffic volumes, yard access, and neighborhood greenness was associated with outdoor time in early to mid-childhood and adolescence. Lee et al. [20] identified individual, parental, home, and community physical and social factors, influencing outdoor play and time for 3–12-year-olds. Neighborhood characteristics, including learning and recreation destinations, play space, playgrounds, yards, sidewalks, roundabouts, and low traffic–volume roads were associated with more, and walkability, traffic crash density, and intersections with less outdoor play or time [20]. In a review including 7–14 year-olds, traffic safety, social safety, social norms, cohesion, and playmates, parks and greenspace were correlated with outdoor play [21]. The magnitude and direction of effects on child movement behaviors have been shown to vary by age. High intersection density was associated with significantly less physical activity in 4-year-old boys, but more in 14-year-old boys [23], and proximity was more important than park size or amenities for 3–5-year-olds compared to older children [24]. These differences reflect the shifting dynamics of child motivations and abilities and parental control and perceptions of risk across developmental stages. Given the importance of experiences and environments to early development, a comprehensive understanding of how neighborhood environments uniquely influence young children’s outdoor free play is needed to inform inclusive urban policy and design. To our knowledge, no review has yet examined literature on this topic specifically in early childhood. To address this gap, we systematically review and synthesize evidence for neighborhood built environment influences on outdoor free play in children, 0–6 years, considering potential differences across gender, culture, and geography. We synthesize quantitative, qualitative, and mixed methods evidence to address the questions:

  1. 1.

    What features or characteristics of neighborhood built environments influence outdoor free play for children, ages 6 and under?

  2. 2.

    What features or characteristics of neighborhood built environments act as motivators, facilitators, or barriers to outdoor free play for children, ages 6 and under?

  3. 3.

    How do neighborhood built environment influences on young children’s outdoor free play differ across child gender, cultures, and geographies?

Methods

Search Strategy

We prospectively registered our review protocol (PROSPERO, CRD42020173288) and searched seven research databases: Avery Index, ERIC, MEDLINE, CINAHL, PsycInfo, SportDiscus, and Web of Science for empirical research from peer-reviewed journals, theses, and dissertations without time period or language restrictions to September 26, 2022. We hand-searched Children, Youth, and Environments (CYE is not indexed in the searched databases), consulted experts, and carried out forward/backward citation tracking of included papers to identify additional relevant articles. This yielded 18 studies for screening, of which two from CYE met inclusion criteria.

Inclusion and Exclusion Criteria

The search strategy included terms related to the population, children, 0–6 years; the exposure, neighborhood built environments and the outcome, outdoor free play (Table 1, Supplementary File 1).

Table 1 Review search terms and inclusion and exclusion criteria
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We define outdoor free play as child-directed, outdoor activities outside of school hours or organized and adult-directed settings. This definition includes active play but does not require that children necessarily engage in physical activity: child-motivated engagement in social or focused, non-physically active outdoor pursuits, such as “playing house,” building pebble towers, or watching ants is included. This definition excludes activities that involve electronic devices. We limited our review to outdoor play outside of formal programs as their context and content may affect children’s access and use of outdoor environments. We included physical activity as an outcome only when specific to OFP. Gender is a social construct assumed to be aligned with sex at birth due to the young age group in this study. Neighborhoods were considered to be the area around residence as defined by the included studies. Built environments included external features and functions of buildings, streets, open space, and infrastructure at various scales. We included urban or suburban and excluded rural study contexts, to focus on environments largely shaped by modifiable human activities and structures.

Study Selection

Two authors independently screened titles and abstracts and reviewed full texts, following inclusion and exclusion criteria (Table 1) and using Covidence 2.0 systematic review software [25], resolving disparities through discussion. Following the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines, the search and selection process is summarized in Fig. 1 [26].

Fig. 1
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PRISMA flow diagram for article screening and selection

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Data Extraction and Quality Assessment

We developed and refined the data collection by piloting independent extraction of 5 papers by two reviewers, focusing on age group and outcomes relevant to the research questions (Supplementary File 2). Subsequently, one reviewer extracted and a second reviewed all data, resolving discrepancies through discussion.

Two authors independently assessed the quality of included studies using the Mixed Methods Appraisal Tool (MMAT) [27] resolving differences through discussion. The MMAT assesses methodological quality of quantitative, qualitative, and mixed methods studies with demonstrated reliability and efficiency [28, 29]. Designation of low, medium, and high quality were based on a study meeting ≤ 40%, 60–80% or 100% of MMAT criteria, respectively (Supplementary File 1).

Analysis and Synthesis

One author inductively coded study findings using NVIVO 12 software [30], transforming quantitative results by categorizing findings into qualitative codes [31, 32]. The second author independently coded every 5th paper to support validity of emergent themes. We aggregated inductive codes into descriptive themes [33], identifying convergence/divergence in findings across gender, culture, and geography and documenting emerging secondary findings through memo-ing. Drawing on inductive codes and memos, we developed analytic themes within the framework of the research questions [33]. We considered quantitative studies for meta-analysis; however, this was not feasible due to heterogeneity of exposures and outcomes. We kept detailed notes throughout to provide a contemporaneous account of analytic and reflexive processes.

Results

We assessed 5,740 non-duplicate studies and included 53, representing 24,792 parents, children, or parent/child dyads from 28 quantitative, 19 qualitative, and six mixed-methods studies. Studies were conducted in 17 countries: Australia, 13; USA, 10; Netherlands, 5; China, 4; New Zealand, 3; Canada, 3; South Africa, 2; Ireland, 2; UK, 2; one in each of Germany, Jordan, Malaysia, Portugal, Turkey, and Denmark; and three in multiple countries: Italy-Denmark-Poland, USA-Denmark, and Italy-Ireland. Quantitative studies were mostly cross-sectional, assessing associations between parent-reported or objectively measured neighborhood characteristics and children’s OFP, or reporting OFP frequency in different environments or with different affordances. Outcomes were frequency and/or duration of outdoor play, active play, parent–child coactivity, or physical activity (in the context of OFP). Qualitative studies explored parent and/or child perceptions of neighborhood influences on OFP. A majority of studies focused on the 2 to 6 age range; among studies that included children under 2 [34–39], only four reported findings for this group separately from older children [34, 35, 38, 39]. Thus, findings below apply to children between 2 and 6, unless otherwise specified.

Proportionate agreement was high for screening (title/abstract 0.95, full text 0.81) and inter-rater reliability fair for title/abstract and moderate for full-text review (Cohen’s Kappa 0.34 and 0.58, respectively). Screening decisions were skewed toward exclusions, yielding a lower measure of inter-rater reliability (Cohen’s Kappa) despite high agreement [40, 41]. We assessed 21 studies as high, 22 as medium, and 10 as low quality (Table 2). Assessment of low quality was most often due to insufficient detail in methods, high bias risk, or potential confounders missing from analysis. Quality of evidence for built environment influences on OFP is considered in Table 3.

Table 2 Characteristics of included studies
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Table 3 Evidence summary for neighborhood built environment features and outdoor free play of young children
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Thematic Synthesis

Three interconnected themes emerged from a synthesis of study findings. Features of space for play; routes and social environments intersected to influence availability, accessibility, and acceptability [42] of neighborhoods for young children’s OFP. We organized results around these intersections, considering the convergence or divergence of findings across gender, cultural, and geographic contexts (Fig. 2). Evidence summary for built environment influences on OFP is given in Table 3.

Fig. 2
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Availability, accessibility, and acceptability of neighborhood space for play

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Availability of Neighborhood Outdoor Space for Play

Parks and Playgrounds

Close proximity of parks and playgrounds to home or daily destinations supported young children’s OFP across contexts [24, 34, 43, 44–48]. Playgrounds were key motivators to active OFP among 4–6-year-old Malaysian children and park, or playground use was associated with OFP in Ireland [49] while long distance to parks or playgrounds was a barrier in the UK, USA, Jordan, Italy, and Denmark [34, 48, 50–52]. New UK immigrants considered greenspace within a 20-min walk to be useable [34]. Canadian parents perceived parks and playgrounds to be neighborhood destinations most relevant to 3–4-year-olds’ active play [53]. OFP mediated the relationship between nearby recreation facilities and preschoolers’ PA in Tianjin, China [54], and parks visited by 3–5-year-olds were closer to home than those visited at older ages, despite being smaller and lacking the same amenities [24]. For some, parks provided the only outdoor space with room to run [46, 47]. However, for US children from low-income families, having a park within walking distance was not related to weekday OFP [55].

Home Yards

Presence of a home yard was associated with ≥ 2 h of OFP in a US survey of parents with preschoolers in Head Start programs [55], and lack of a yard was cited as a reason for less play outdoors in Italy and Australia [44, 52]. Conversely, higher OFP among 4–6-year-old girls was seen with absence of private gardens in Dutch cities [56]. In the context of Covid-19 lockdowns in Italy and Ireland, garden/yard spaces were more important for OFP in 4–6-year-olds than older children [57].

Informal Space

Fourteen studies directly included child perspectives [35, 37, 46, 51, 57–66]. Young children’s conception of “play space” differed from that of adults; they viewed all spaces as potentially playable, engaging with their surroundings wherever possible [47, 51, 62, 67]. Children’s perception of neighborhoods seemed to be relationally, rather than spatially, defined: their neighborhoods were those spaces around home where interactions with people, plants, animals, buildings, destinations, and routes were possible [62]. When accessible to them, children valued paths, streets, sidewalks, and open squares for play, with amenities such as bike racks, bushes, or puddles incorporated into OFP [47, 51, 62, 67]. In Jordan, children were drawn to streets, sidewalks, and house entrances as places to meet friends and watch people, enjoying being “…where the action is, where the life of the community takes place…” [51 p. 821]. For young children, characteristics of and interactions along routes could be as important as destinations [67].

Neighborhood Design and Housing Type

Neighborhood design and housing type influence the amount and type of outdoor space available. In Vancouver, Canada, limited private outdoor space increased demand for public outdoor spaces [47]. Children in a higher-density Australian suburb (closer to city center) utilized parks or playgrounds, while those in lower-density, outer suburbs usually played in home yards [67]. In US settings, proximity of park was less important than in Denmark, where denser, more connected neighborhoods are common [48], and home yard but not distance to park or playground was associated with OFP [55].

Associations between housing type and OFP were largely inconsistent across the studies reviewed. In an Australian city, free-standing homes were associated with more OFP [68], but linked to less OFP among young girls in Dutch cities [56]. Duplex, townhome, or rowhomes were associated with lower OFP compared to single-family homes in the USA while semi-detached, duplex, or rental properties were associated with more OFP among 4–6-year-old boys in Dutch cities [56]. Kimbro et al. [69] found that US preschoolers in public housing played outdoors more than those in non-public housing. Residence in apartments or high rises in Dutch and US contexts was associated with less OFP [56, 69] and cited as a barrier among low-income immigrants in the UK [34]; however, the degree of high- vs. low-rise neighborhood buildings was not related to OFP in Dutch cities [56].

Accessibility: the Interaction between Routes, Social Environment, and Space for Play

Routes to Spaces for Play

Use of parks, playgrounds, and greenspaces was determined not only by presence of these spaces in the neighborhood, but also by the characteristics of routes and surroundings. Not surprisingly, high-traffic streets were the most common physical environment barrier to OFP across contexts [34, 35, 43, 47, 51, 52, 56, 61, 67, 70, 71]. Pedestrian infrastructure including sidewalks, bike, and walking paths were associated with more OFP in some [43, 70, 72, 73], though not all studies [56, 74]. Parent perception of unsafe walking or cycling due to high traffic was associated with less OFP [49], and bike tracks next to busy roads were cited as barriers [44]. Parents considered sidewalks, trails, and quiet streets as neighborhood factors with most relevance to OFP in 3–4-year-olds (over main roads, cul-de-sacs, and block length) [53]. Having to cross a street to access parks resulted in lower park visitation [48, 70], and preschool-age children visited parks with fewer adjacent road-crossing signals compared to older children [24].

Measures of walkability varied in content and scale across studies. Sidewalks, pedestrian crossings, markings, traffic control signals, or stop signs in residential block were associated with frequent park use [24], and greenspaces on the way to destinations such as child care, school, or shops facilitated OFP [45–47]. However, nearby shops were not significantly associated with OFP in another study, after adjustment for individual and socio-cultural factors [73], and suburb-level walkability based on distance to local amenities showed no significant relationship with OFP at 2 and 3.5 years [68].

Social Influences on Access to Play Space

The neighborhood social and historical context influenced OFP: in South Africa, Benwell [61] and Klingberg et al. [75] describe how systemic inequities shape social context, influencing parental perceptions of safety, fear of crime, and trust in neighbors. In a low-income, racialized community in the USA, no OFP was allowed at all because of fears of violence, crime, or hazards related to needles and other debris, despite availability of yard space [64]; conversely, higher parental safety perception was associated with park use among 3–5-year-olds [76]. Immigrant status could also influence children’s access to play. Unfamiliarity with public greenspace locations and bus routes and fear of trespassing limited new UK immigrants’ greenspace use [34], while some US newcomers avoided social connections due to undocumented status and fear of deportation [77]. Not knowing neighbors was a barrier, while trusting neighbors, social connections, social cohesion, and collective efficacy supported OFP across contexts [34, 50, 52–54, 61, 67, 69, 71, 77, 78].

Family context strongly influenced children’s OFP: Remmers et al. [79] found that family characteristics, but not parental perceptions of the physical environment, predicted child OFP. In China, caregivers were often grandparents, whose physical tiredness, heightened sense of responsibility, and safety concerns could limit children’s OFP [35]. Family context interacted with physical environments: lack of nearby space for OFP and social connection compounded stress from financial insecurity, minority group membership, and separation from familiar culture, language, and family among new immigrants [34, 50, 77]. Because young children’s OFP usually requires adult accompaniment, long work days, parental exhaustion, mental health issues, or preoccupation with financial survival could limit OFP [34, 44, 58, 77].

Acceptability: Parent and Child Perceptions of Neighborhood Space for Outdoor Play

Green and Natural Space for Play

Higher neighborhood greenness (assessed using Normalized Difference Vegetation Index, NDVI) was associated with more quiet and active OFP in five US counties [80]. However, in green, affluent Australian neighborhoods, no association between yard greenness (NDVI) and OFP was found [81]. Park use was higher in areas with more trees and greenspace [36], while lack of greenspace was a barrier to child and parent outdoor physical activity [45]. Across contexts, young children were attracted to natural environments; trees, flowers, leaves, sand, sticks, and natural play materials were motivators to OFP [34, 37, 46, 48, 58, 62]. Trees were the most common natural object in playground drawings by Syrian refugee children [65]. Interaction with nature, even in small, informal areas such as planters [63] or traffic roundabouts [47] were highly valued, and children were fascinated by animals: ducks, squirrels, dogs, birds, and insects [34, 58, 63, 65, 82]. Though parents and children sometimes had safety concerns about dogs [62, 67], presence of dog waste was associated with more OFP among 4–6-year-old girls [56].

Quality and Affordances of Space for Play

Outdoor spaces that met the needs of both parents and children facilitated OFP. Pleasant, quiet, natural spaces and presence of other adults with children could support parents’ own physical, social, and mental health, decreasing parental stress and isolation while supporting children’s OFP [34, 44, 47, 48].

Nearby traffic posed safety concerns and limited yard or park use [44, 45, 49]. Fencing increased perception of play space safety [45, 47, 63] but was sometimes less esthetically pleasing [37]. Park size was unrelated to observed number of preschoolers [83], and park proximity, but not size or amenities, was associated with preschoolers’ park use [24]. For families with dogs, larger yard size could facilitate or decrease preschoolers’ OFP, providing play space or decreasing motivation for dog walking [43]. However, Spurrier [84] found no relationship between yard size and OFP after adjusting for other features while Oakley [81] found minimal (0.4 min/day) increases in OFP with each 10% increase in yard size.

Parents and caregivers across contexts were concerned about shade, seating, facilities (e.g., toilets, drinking water), safety, cleanliness, and overcrowding of play spaces [34–37, 43, 44, 47, 48, 58, 77, 85, 86]. Lack of variety in play equipment or perception that a play space was boring could limit OFP [44]. Inadequate play equipment for infants and children under two was a recurring issue [34, 37, 47, 48]. Destinations with affordances for both dogs and preschoolers supported OFP in an Australian context [43]. Preschool children were attracted to places that afforded physical challenge, play at heights, and with speed (e.g., trees, slides, swings, climbing structures) [46, 47, 62, 63, 65, 66, 87, 88]. More play equipment in home yards was associated with more OFP [84, 89], but even with extensive play equipment, yards could be perceived by children as isolating or boring [61].

Neighborhood disorder, unoccupied homes, poor building conditions, and presence of trash were generally associated with more OFP [56, 69, 70]. In Ireland, higher neighborhood deprivation was associated with lower participation in structured activities but not active play [49]. In Vancouver, Canada, dangerous litter (e.g., needles), but not graffiti, was perceived negatively; however, parents in Edmonton, Canada, considered neighborhood cleanliness and no graffiti to support OFP [47, 53]. In a US city, presence of trash, graffiti and vandalism enforced perceptions of social danger, prompting parents to limit OFP [64].

Opportunity for Social Interaction

Across contexts, parents and children emphasized that opportunity for neighborhood social interactions supported OFP [44, 45, 47, 51, 53, 57, 58, 61, 63, 66, 67, 90]. Built environment features such as quiet streets [45], enclosed street designs (no through traffic) [67], home zones (traffic-calmed, residential street shared by pedestrians and vehicles) [72], temporary play spaces [63], and interesting routes [62, 67] created safe, inviting space for meeting neighbors, and the presence of children in these spaces could increase perceptions of social safety [47]. During Covid-19 lockdowns, 4–6-year-olds expressed more concern about inability to meet friends outside than did older children [57]. Public space for play with non-related children was important to many children in China because of social policies encouraging smaller families [58] and for single-child families in Canada [47]. Parks also provided space for family togetherness [58, 90]. A 6-year-old expressed:

My father works in a company in another city to make money. My mother stays alone in Guangzhou to take care of me. Only at the weekend, when we get together in the park, can I feel real happiness… [51, p. 469].

Qualitative evidence consistently emphasized the importance of other children to OFP [45, 51, 53, 61, 65, 67, 71, 90]. Preschoolers’ ideas for future playgrounds revolved around increasing opportunities for play with friends [90]. In a lower-density suburb, parents identified a lack of nearby children as a barrier [67]; however, quantitative measures of density showed no clear relationship with OFP: same-age residential density was not associated with play density (children per 100 m2) [83]. Residential density (based on occurrence of housing types) and suburb-level residential density (persons per hectare) showed no association with OFP [68, 72]. Though presence of other children generally supported OFP, parental perception that a play space was overcrowded could negatively impact use [34, 47, 58].

Built Environments and Outdoor Play across Cultures, Geographies, and Gender

Cultural and Geographic Differences

Major built environment facilitators of OFP: presence of outdoor space to play, natural environments, and safe routes were consistent across ethnic and cultural groups. However, some specific features (e.g., dog parks) were relevant only in some contexts due to societal norms [43], and physical disorder was an inconsistent marker of social danger across contexts [47, 64]. Additionally, variation was seen in parental values, priorities, and preferences: connection with nature was highly rated by Dutch parents, while opportunity for physical activity was more important for Americans [48]. Mexican–American parents valued park facilities, affordances, and activities while White Americans rated safety, proximity, cost, uncrowded space, and friends higher, highlighting the importance of understanding the priorities of local users [86]. Middle Eastern families in Australia described prioritizing academics as a barrier to OFP, and parental emphasis on academics was linked to less outdoor playtime in a large Chinese city [71, 73]. Some Chinese parents in Australia considered being overprotective to be a cultural trait and made conscious efforts to prioritize active play [71]. Chinese parents in Malaysia expressed less worry about child safety than did Malay parents; however, their children played mostly within house compounds while Malay children played mostly in public parks [78]. In a large, Midwestern US city, though children strongly desired play with friends, play with unknown children was not allowed or preferred [90]. In contrast, at a park in Guangzhou, China, children readily made new friends, played cooperatively, and made plans for future play [58].

Cold, wet, and windy weather or short days in northern latitudes limited OFP [34, 35, 44, 69], while heat and/or shade were concerns across diverse geographies, particularly for parents with infants and toddlers [36, 44, 47, 48, 58, 86].

Gender Differences

We did not find consistent differences in built environment influences on OFP across genders. However, studies that examined gender differences in OFP generally found that boys played outdoors more, or more actively, than girls [44, 56, 72, 73, 78, 80, 91]. Heterogeneity in study design, measures, or descriptions of neighborhood features made comparison of gender-related findings across studies challenging. Aarts et al. [72] found that specific pedestrian or traffic calming features were associated with higher (pedestrian crossings with lights, home zones, roundabouts) or lower (street lighting) OFP in boys, but not girls, while some features were linked only with girls’ OFP (pedestrian crossings without lights) [72]. In another analysis, housing-type associations with OFP varied by gender [56]. Parental perceptions of safety for OFP may differ between genders: Remmers and colleagues [79] found that boys’ parents perceived higher outdoor safety in the evening compared to girls’ parents. Interestingly, infant boys (0–1 years) played significantly more with natural materials in New Zealand parks than did infant girls [38]. Since infants are not independently mobile and usually heavily supervised, it is not clear if differences were due to child preference or parent facilitation [38]. The impact of social norms and adult gender modeling was evident among preschool-age girls in a US study, with one child remarking,

“Little girls can beat boys at gym, but when you get older it ain't important and you don’t try.” [64, p. 152]

Discussion

We aimed to synthesize current evidence for neighborhood built environment influences on outdoor free play in children, ages 0–6, across genders and diverse urban/suburban contexts. Our findings support a conception of playable neighborhoods as networks of physically and socially safe and engaging routes and spaces. Availability, accessibility, and acceptability of neighborhood space for play was influenced by the intersecting features of spaces, routes, and social environments. Across widely diverse cultural and geographic settings, neighborhood space for play, green and natural environments, traffic and pedestrian environments, and neighborhood designs that facilitate social connection with neighbors support young children’s OFP across contexts.

Our review highlights the importance of the first requirement for OFP: the simple availability of space, either formally designated or informal areas adapted for play, close to home. Accessibility and use of nearby playable space often depended on characteristics of routes and traffic environments. Acceptability of neighborhood space for play was related to perceptions of social safety, greenness, natural features (especially trees) and shade, park facilities, variety of affordances, seating, and opportunity to play with other children. Though built environment influences on OFP generally align with those identified in reviews with older children [19–21], some important differences emerged. Small-scale, simple features (e.g., small parks, bike racks, planters, puddles), and informal play spaces can provide important play opportunities for toddlers and preschoolers. All ages face barriers to OFP from traffic and social safety concerns; however, young children’s access to neighborhood routes and space is often more severely limited by these factors. Need for parental supervision, play space proximity, parental time constraints, mental and physical health, motivation, and enjoyment of outdoor spaces may more strongly influence opportunity for OFP in young children. Thus, environments that also appeal to adults may be more important to OFP in early childhood. Reviewed studies largely focused on 2–6 year-olds; few examined or reported correlates of OFP for children under 2. Infants’ interactions with neighborhood environments are completely dependent on caregiver ability, initiative, time, and preferences. Qualitative findings from our review suggest that benefits to infants may be closely linked to parental benefits derived from social connections, exposure to nature, and physical activity in supportive neighborhood environments [34, 50]. Future studies are needed to examine neighborhood features that support parent-infant outdoor co-activity and impact of these activities and exposures on infant health and development.

Though we focused on neighborhood built environments, physical features interact with family and neighborhood context and cannot be considered in isolation from these powerful determinants of young children’s OFP. Though the effects of poverty and systemic inequities extend far beyond it, they may be manifested in physical environments [92]. In our review, built environments interacted with social realities of poverty or marginalization to limit OFP. For instance, lack of nearby playable space contributed to social isolation and less OFP among new immigrants’ children. Conversely, neighborhood features that facilitated neighborhood interaction could foster a sense of social safety and social connection that supported OFP. We found no consistent differences in built environment influences on young children’s OFP across genders, but some evidence for social norms and gender modeling as barriers to preschool girls’ OFP. Further investigation is warranted to examine social influences on gendered disparities in OFP.

Both theoretical and practical insights emerged from our evidence synthesis. From major themes, we developed a simple framework to conceptualize the interacting characteristics that influence young children’s OFP. Our review highlights the contrast between child perspectives and adult assumptions of child-friendly space. Across contexts, young children desired interactions with local places and people. Active play has often been viewed as a tool for health promotion and disease prevention [93]. However, Lester and Russell argue against the conceptualization of play as a set of activities that address adult concerns but rather for the creation of “health-enabling” spaces that provide opportunity, challenge, and inspiration for children to engage in free play in everyday settings [94]. Blinkert and Weaver suggest that adults’ role may be simply to protect children’s right to engage with local environments [95]. Practically, our findings suggest that urban design for children must move beyond providing play destinations and toward creating playable networks, affording young children access to experiences and opportunities for interacting with local nature, structures, and people.

A major strength was this review’s methodological approach: thematic synthesis of qualitative, quantitative, and mixed methods evidence enabled a comprehensive view of young children’s interactions with neighborhood environments. Qualitative evidence illuminates complex and multi-level factors influencing OFP and incorporates children’s perspectives in their own words. The inclusive search strategy, without language restrictions and including screening of non-English papers, maximized context diversity. Independent screening, review, and quality assessment of all, and double coding of a subset of studies strengthened the reliability of findings.

This review had some important limitations. Among evidence from 17 countries, westernized nations were overrepresented, and no studies from Central Asia and Central or South America met inclusion criteria; thus, our synthesis is lacking input from these unique physical and social settings. Though common to young children across contexts [96], measuring and operationalizing free play is challenging. Outdoor play at young ages is usually supervised, and studies did not always specify “unstructured,” “child-directed,” or “free play” but was considered to be free play if outside structured, adult-directed settings. Built environment terms or meanings may differ across contexts or vary in measurement method or contributing to inconsistent findings for similar features. Despite this heterogeneity, our findings converged around the major themes across widely diverse settings.

Conclusion

Across child gender and diverse cultural and geographic contexts, playable neighborhoods for young children provide formal or informal space for play, traffic-protected routes, and access to nature and facilitate social connection. Family and community-level social factors interact with built environments, influencing access to and engagement in outdoor free play. Efforts to standardize terms and measurements across built environment studies are needed, and socio-cultural influences on child movement behaviors across genders should be considered in future work. Research in non-westernized urban settings is needed to better understand influences on outdoor free play in these contexts. Considering young children’s needs and perspectives in the design of urban and suburban neighborhoods can inform the creation of everyday environments that support optimal child health and development and more equitable, inclusive cities.