The purpose of this paper is to provide an overview of a study protocol designed to elicit fitness effects in obese children through a family-based approach. Whereas, previous ecological interventions for physical activity have utilized school-based settings, this study targets the family unit, thereby having a potential effect on multiple mircosystems and mesosystems. Design: Families with at least one parent, that identified as sedentary and was willing to participate, and at least one child who was considered overweight or obese (85th percentile for BMI) were invited to participate. Families were asked to come once weekly for a 60-90 minute session involving separate but concurrently running exercise sessions for children and adults, parental health education, and family group session for 9 weeks. Methods: Variables of interest included physical activity, body composition (lean mass, fat mass, and bone mineral content), motivation, parental perception of their child’s competence, parental self-efficacy, child perceived competence, child self-efficacy, and the child proxy efficacy. Semi-structured interviews were conducted with the children and parents to explore the implementation of structure and learned strategies within the household.