Researchers have found positive associations between physical activity and executive function in adolescence and adulthood. However, research in early childhood has revealed only negative relationships. In the present study, I explored whether maternal encouragement of physical activity might moderate this relationship in very young children. Using video recordings from an archival dataset, eight maternal encouragement measures were derived from mother-child free play sessions. Although it was expected that maternal encouragement of child activity would broadly play a moderating role in the relationship between children’s physical activity and their executive function, only maternal questions seemed to moderate this relationship. One explanation for these overarching null findings is that maternal encouragement of physical activity may not have a moderating effect until later, such as when children are well on their way into language. Future efforts to explore the impacts of physical activity on executive function may benefit from experimental approaches.