With the declining birth rates and urbanization-aggravated climate stresses, safeguarding children’s health requires child-centric urban planning due to their heightened physiological vulnerability. Current high-resolution data on children’s heat and air pollution dual exposure risks remain scarce. This study systematically reviews exposure assessment components—data sources, methodologies, and mitigation strategies—for outdoor activity contexts. We propose a multilevel assessment framework integrating multi-source urban data with dynamic exposure models at individual-regional scales. Key findings reveal that children’s unique physiological parameters critically modify exposure outcomes, with high-risk hotspots concentrated near schools, playgrounds, and transportation corridors. Cumulative exposure models incorporating microclimate variability are more accurate than static evaluations in predicting health impacts. The study advocates integrating real-time environmental monitoring with big behavioral data to develop adaptive outdoor activity guidelines and urban design principles that minimize environmental risks. Results highlight the necessity of redefining “child-friendly cities” through dual environmental-behavioral lenses to balance urban development and intergenerational health equity.