This study explored the participation of children in walking and bicycling for transportation, school, and various leisure purposes, and the relation with social and physical environmental characteristics and sociodemographics. Detailed individual travel data, including all walking and bicycling trips from a random sample of 4,293 children in the primary-school-age category in the Netherlands were investigated. Specifically, a Bayesian belief network was proposed that derives and represents all direct and indirect relations between the variables. The participation in active travel behavior has a direct relationship with all trip characteristics such as travel time and distance, and trip purpose, and is related to the car possession of the household. The degree of urbanization also is an important explanatory variable for participation in walking and bicycling by children. All the other social and physical environmental characteristics have an indirect influence on travel mode choice.