This study examines where children play in a city undergoing rapid urbanization and how they perceive these places. Three hundred twenty-seven children aged 10 to 13 in Yantai, China engaged in web-based participatory mapping to identify play places and bad places and to provide perceptions about these places. Results showed that play places were clustered around existing public places, and children in the periphery of the city traveled longer distances to reach play places. In addition, play places and bad places overlapped, indicating that children had concerns about existing play spaces. Children mentioned destination, social interaction, and proximity to home as reasons for playing in a place, whereas risk of traffic and strangers, low air quality, and unfamiliarity were perceived as barriers. We conclude that the web-based participatory mapping tool we used is a promising approach to empower children as active researchers, and the knowledge about childrens environmental perception can support evidence-based design and planning.