Children and youth participate in physical activities to develop and demonstrate physical competence, attain social acceptance and approval, and experience enjoyment. Satisfying these motives enhances interest in sustaining physical activity, which contributes to improved motor skills, self-confidence, social relationships, and other positive outcomes. My essay explores motor skill development and youth physical activity through a social psychological lens and the benefits of integrating scientific knowledge from our respective fields to inform research and professional practice. Motor development and sport psychology researchers can collaborate to address critical issues related to motor and perceived competence and physical activity. I recommend five ways for integrating knowledge: (1) applying social psychological theory to guide research questions, (2) using more longitudinal designs, (3) using a variety of quantitative and qualitative methods, (4) designing studies on physical literacy, and (5) employing a positive youth development (PYD) approach for improving motor and social-emotional skills. These efforts can assist teachers, coaches, and parents in creating opportunities for youth to learn and improve fundamental motor and sport skills and to achieve feelings of competence, autonomy, relatedness, and joy for motivating a lifetime of physical activity.