Flexibility in work schedules is key to helping parents with young children balance work and caregiving responsibilities. Prior research shows that work schedule inflexibility is associated with greater parenting stress and work-family conflict. Through these negative implications for parental wellbeing, work schedule inflexibility may also adversely influence children's socioemotional development. This study uses data from an urban, birth-cohort sample of children born to predominantly unmarried parents, the Fragile Families and Child Wellbeing study, to test the hypothesis that mothers' perceived work schedule inflexibility is associated with children's behavior problems at age 5. Results from lagged dependent variable models suggest that mothers' high work schedule inflexibility was associated with more externalizing and internalizing behavior problems in their children, relative to experiencing low inflexibility. These associations were partially mediated by mothers' parenting stress and depressive symptoms, and for externalizing behaviors only, these associations were concentrated among single-mother and low-income families.