Background: Parents are believed to play a pivotal role in their children’s health-related behaviors, including physical activity (PA). It is currently unclear, however, at what developmental period parental socialization has the strongest influence on child and/or adolescent PA levels. The purpose of this study was to take a developmental approach to examine parental influence on children’s PA levels over time. Methods: Parents (N = 70; 68 mothers) completed a questionnaire assessing PA habits, amount of time they engage in PA with their child, and reasons for their child’s PA participation at baseline (during child’s preschool years) and at follow-up, which occurred from 1 to 9 years later. Results: The results indicate that the relationship between parents’ and children’s physical activity patterns and parents’ reasons for their children’s participation in organized physical activity change over time. Parents also reported spending approximately 60 min per week engaged in physical activity together with their children at baseline compared with 40 min at follow-up. Conclusions: These findings help to extend previous research examining parental influences on children’s physical activity participation.