Stress can detrimentally affect physical and mental health, especially during childhood. During this critical period, parental bonds can foster resilience or amplify stress. This study explored whether mothers' everyday stress can act as a source of childhood stress, affecting children's executive functioning. 76 healthy mother-child dyads participated, with mothers assigned to a stress-inducing or stress-free condition. Children observed their mothers and were subsequently tested for cognitive flexibility and working memory. Subjective stress, heart rate, and cortisol were measured repeatedly in mothers and children, alongside everyday stress perceptions. Linear mixed models showed that children's acute stress response was associated with impaired cognitive flexibility. Maternal stress, both acute and past-month, was a better predictor of children's cognitive performance than children's own stress. Quadratic relationships indicated the highest error rates at very low and high maternal stress. We found no evidence that children's working memory was impaired by their own or their mothers' stress. Although expected covariations of acute or prolonged stress between mothers and children were not observed, an interaction between maternal past-month stress and acute stress condition provided insights into adaptive mechanisms in children. These findings underscore the significant impact of maternal stress on children's executive functioning, illustrating how parental experiences shape children's everyday outcomes.