As the most likely primary caregivers, mothers are an integral part of children’s social influence and are therefore greatly involved in shaping their children’s behaviors. The objectives were to determine the prospective associations between maternal and child diet quality and sedentary behaviors. This study, within the framework of a community-based intervention study, included 1130 children aged 8–10 years and their mothers. The study was carried out during two academic years (2012/2014) with a mean follow-up of 15 months. Exposure and outcome variables were measured at baseline and follow-up, respectively. Diet quality was assessed by the KIDMED questionnaire and the short Diet Quality Screener, respectively. Sedentary behaviors were determined by standardized questions of sedentary behaviors. Maternal consumption of fruits, vegetables, fish, legumes, pasta/rice, dairy products, nuts and baked goods were positively associated (p < 0.05) with the corresponding child behavior. Multiple linear regression models adjusted for sex, age, maternal education and intervention group revealed significant cross-sectional (p < 0.005) and prospective (p < 0.01) associations between maternal and child overall diet quality and sedentary behaviors. Maternal diet quality and sedentary behaviors were predictive for these lifestyle behaviors in children.