["American Journal of Biological Anthropology, Volume 190, Issue 2, June 2026. ", "\nABSTRACT\n\nObjectives\nAlthough increasing attention has been directed toward childhood physical activity (PA) in small‐scale societies of the Global South, evidence across the full developmental span remains limited and is often interpreted without sufficient attention to local parental environments, norms, or children's social roles. This study examines PA among pastoralist Maasai children in southern Kenya from an ecocultural perspective.\n\n\nMaterials and Methods\nPA and sedentary behavior were assessed in 180 children aged 2–18 years using waist‐worn three‐axis accelerometers, which enabled comparisons across age, sex, day type, and school attendance. Quantitative data were complemented by long‐term ethnographic fieldwork on children's daily routines and parental practices, providing context for the developmental niche.\n\n\nResults\nMaasai children demonstrated consistently high levels of moderate‐to‐vigorous physical activity (MVPA) across all ages. Mean MVPA rose from 89 min/day (ages 2–5) to 130–143 min/day (ages 6–12), accompanied by 17,000–21,000 steps/day. Boys were generally more active than girls. Variation by school attendance reflected local norms emphasizing childhood autonomy, staged social participation, and engagement with the landscape through daily tasks and play.\n\n\nDiscussion\nThese findings provide the first comprehensive assessment of childhood PA across the full developmental span of a pastoralist Maasai community. Children's high activity levels are sustained within culturally meaningful developmental niches that foster autonomy and embodied engagement with the land, alongside contemporary transitions such as schooling. The study underscores the importance of etic–emic integration for understanding childhood PA in small‐scale societies.\n\n"]