There is a persistent concern about child obesity in many countries, and this concern is growing in Japan. Although there is a vast literature on the associations between child obesity and maternal employment, how mothers’ specific work schedules affect child obesity has yet to be explored. The aim of our study is to empirically examine how maternal work schedules are related to child obesity. Specifically, we focus on mothers’ timing of returning home from work. We conduct regression analysis using data from the Longitudinal Survey of Newborns in the 21st Century. Our outcome variables include the BMI for age z-score and indicators of overweight and obesity status. Our findings indicate that children’s BMI tends to be higher, and they are more likely to be overweight and obese when their mothers return home from work later. We also find these associations vary with the age of children and between girls and boys.