Despite the benefits of engaging in physical activity during their leisure time, children do not meet the recommendations on physical activity. Following the socio-ecological model as a theoretical framework, the aim of this study was to determine the barriers and facilitators that influence physical activity participation in children’s leisure time. Data collection was conducted through focus groups and individual drawings in a sample of 98 eight- to eleven-year-olds from six schools in Cuenca (Spain). Following the socio-ecological model, individual characteristics (age and sex), as well as the microsystem (parents and friends), mesosystem (timing and out-of-school schedule) and exosystem (safety and weather) influence physical activity participation. The relationships between these levels of the socio-ecological model reveal that opportunities for leisure physical activity are determined by children’s schedules. This schedule is negotiated by the family and is influenced by parents’ worries and necessities. This is the main barrier to physical activity participation due to the creation of more restrictive, sedentary schedules, especially for girls. Our results show the elements required to develop successful strategies to increase physical activity opportunities, namely, focusing on giving children the opportunity to choose activities, raising parents’ awareness of the importance of physical activity and improving the perceived safety of parks, taking into consideration the gender perspective.