This article adopts a motivational stance in identifying factors that strongly predict physical activity in children. One model for understanding physical activity motivation in children portrays the sources and consequences of self-esteem for physical activity behavior (perceived competency/adequacy, social support, enjoyment, and physical activity behavior). Perceived competence refers to individuals' judgments about their ability in a particular area. Considerable evidence shows that youth who report stronger beliefs about their physical competencies are more likely to enjoy activity and sustain interest in continuing involvement, which in turn enhances motivation to be physically active. Providing enjoyable experiences is a potent strategy for increasing activity levels in youth, their attitude about the value of exercise, and ultimately long-term health outcomes. Research shows that sport commitment is influenced by enjoyment, involvement alternatives, personal investments, social constraints, and involvement opportunities. Significant adults and peers emerge time and again as sources of physical competence and self-worth, sources of enjoyment, and determinants of commitment to activity. Intervention strategies for maintaining and enhancing physical activity motivation in children include: provide optimal challenges, create a mastery motivational climate, make physical activity fun, and help children help themselves. (Contains 37 references.) (SM)