Physical inactivity is one of the leading causes of death in the United States. Prevalence rates of overweight and obesity continue to climb and threaten the health and well being of about 30% of children. Although physical activity can reduce the risk of obesity and other health complications, estimates show that children are largely sedentary. Behavioral interventions targeting physical activity have been implemented to increase physically active behaviors, however, the function of physical activity was not established, possibly contributing to the poor maintenance of such interventions. The purpose of the current study was to conduct a functional analysis to investigate the effects of several consequent variables on moderate-to-vigorous physical activity (MVPA). The level of MVPA exhibited by four pre-school children was observed in four conditions: alone, attention contingent on MVPA, adult interaction contingent on MVPA, and escape from task demands contingent on MVPA. These four conditions were compared to a naturalistic baseline and to a control condition. Overall, the results indicate that the children were most active when interactive play was contingent on MVPA. Such information might be used to arrange social environments that encourage physical activity, especially MVPA, and these arrangements can be tailored to the individual child.