This study examines the relationships among nonresident fathers’ financial support, informal instrumental support, mothers’ parenting and parenting stress, and their children’s behavioral and cognitive development in single-mother families with low income. Informed by stress-coping and social support models, this study estimates the mediating effects of nonresident fathers’ financial support on children’s outcomes transmitted through mothers’ parenting and parenting stress. The analyses use the longitudinal data from a subsample of 679 single mothers in the Fragile Families and Child Wellbeing Study. Results suggest that nonresident fathers’ financial support is directly associated with children’s cognitive development. Nonresident fathers’ financial support is found to have indirect effects on children’s behavior problems and cognitive development transmitted through mothers’ parenting and parenting stress. Informal instrumental support is directly and indirectly associated with both outcomes of children transmitted through maternal economic hardship, parenting, and parenting stress. The study discusses the policy and practice implications of these findings.