Evidence suggests that physical inactivity is increasingly prevalent among young children. A common recommendation provided to parents suggests that they become actively involved in increasing their child’s physical activity. However, this recommendation does not specify how a parent should become involved. Further, the evaluation of parental involvement in children’s physical activity has yet to be conducted. The purpose of the current study was to conduct a functional analysis to identify a social, environmental variable that would engender a higher level of physical activity in young children. Once a social consequence was identified, reinforcement provided contingently on higher levels of physical activity and according to a fixed-time schedule was compared in an intervention analysis. The overall results of the study indicated that children were most active when receiving a form of social reinforcement contingent on higher levels of physical activity. These results suggest that parents of young children should become involved in increasing their child’s physical activity by providing attention or physical engagement contingent on higher levels of physical activity.