Background: Prevalence and consequences of obesity and sedentary lifestyle are well-documented public health concerns for youth in the United States of America (USA) that disproportionally affect children from low income and minority families. Objective: This mixed-method study focused on estimating levels of physical activity and sedentary behavior and prevalence of overweight and obesity among the child members served in one Boys & Girls Club in the Midwest USA. We aimed to better understand opportunities for improving children's engagement in physical activity through focus groups with members, staff, and parents/caregivers of members. Method: Social cognitive learning theory, the ecological model of health behavior, and community based participatory research principles provided the study framework. Members completed assessments of physical activity, sedentary activity, height, and weight. Focus groups with members, staff, and parents/caregivers identified barriers, facilitators, and opportunities for promoting physical activity. Results: Nearly 50% of members were overweight or obese. Most (87%) participants reported at least 60 min physical activity every day across the 3-day recall. Fewer than half (41%) reported 2 h or less of sedentary screen time every day across the 3 day recall. Focus group themes identified opportunities for addressing needs associated with health disparities in physical activity and pediatric obesity. Conclusions: Findings suggest stakeholder interest in physical activity promotion through afterschool programs. We discuss study implications regarding needs specific to individuals from diverse, low-income households that may not be adequately addressed with existing empirically-supported treatments and opportunities to address health disparities in physical activity and pediatric obesity through afterschool programs.