Despite numerous studies on parenting stress suggesting negative influences on parent-child interactions and children's development, the majority of these studies focus on mothers' parenting stress with little or no acknowledgement of fathers. Using data from the National Early Head Start Research and Evaluation Project, this study examined (i) the effects of fathers' parenting stress during toddlerhood on children's language and cognitive outcomes when children are 3years old (ii) whether the effects of fathers' parenting stress on children's language and cognitive development vary by child gender? Results from mixed linear models showed fathers' parenting stress predicted children's lower cognitive scores, but there were no gender differences in the effects of fathers' parenting stress on children's cognitive outcomes. In the language domain, boys, not girls, were found to be more susceptible to the effects of fathers' parenting stress. These findings indicated that fathers, in addition to mothers, should be included in early parenting research and interventions. Copyright (c) 2016 John Wiley & Sons, Ltd.