Young children’s movement behaviour (physical activity, sitting, and sleep) have all been shown to be associated with health and development of young children when looked at independently. Research has shown that there is a positive relationship between parent’s and children’s levels of physical activity; however, most of the time that parents and children spend together is spent sitting. Our research team is interested in increasing physical activity and reduce sedentary time in stay-at-home parents and their young children (aged 3-4 years). Therefore, the purpose of the Active Family study is to examine the effectiveness of a physical activity intervention delivered using smartphones for stay-at-home parents and their young children.