For youth and parents, frequent family meals have been consistently associated with positive dietary outcomes but less consistently associated with lower body mass index (BMI). Researchers have speculated dinnertime context (dinnertime routines, parent dinnertime media use) may interact with family meal frequency to impact associations with BMI. The present study evaluates the associations and interactions between dinnertime context measures and family dinner frequency with parent and child BMI. This cross-sectional study uses baseline data from the Healthy Home Offerings via the Mealtime Environment (HOME) Plus randomized control trial that aimed to prevent childhood obesity. Participants (160 parent–child dyads) completed psychosocial surveys and were measured for height and weight. General linear models tested associations and interactions between dinnertime context measures and family dinner frequency with parent and child BMI, adjusted for race and economic assistance. Lower parent dinnertime media use and higher dinnertime routines were significantly associated with lower child BMI z scores but not parent BMI scores. Interaction–moderation findings suggest higher family dinner frequency amplifies the healthful impact of the dinnertime context on child BMI z scores. Additionally, findings emphasize that promoting frequent family meals along with consistent routines and reduction in parent dinnertime media use may be important for the prevention of childhood obesity.