Physical fitness in childhood consequently affects and determines the risk of acquiring non-communicable diseases in adulthood. Therefore, it is important for children to acquire adequate physical fitness during childhood. It has been reported that children’s physical fitness is related to environmental factors, and one of this is their parents’ health-related lifestyle. This review introduces the findings of the association between parental physical activity and children’s physical fitness. Additionally, we introduced the research conducted by our laboratory on the mothers’ physical activity, which is expected to have a greater impact than that of fathers. Finally, we provide a research plan in progress on the association between maternal physical activity and children’s physical fitness through an adjunct study of the Japan Environment and Children’s Study (JECS), in which our laboratory is participating.