The present study examined children's diurnal cortisol as a moderator of the association between parenting sensitivity at bedtime and young children's executive functioning and emotion regulation. Fifty-one children (M[subscript age] = 4.47 years) and their families participated. Parenting sensitivity was assessed from video recordings of child bedtime. Average child morning and evening cortisol levels were measured from saliva across 3 days. A greater decline in cortisol from morning to evening reflected healthy diurnal patterning. Children's executive functioning was measured objectively, and parents reported on children's emotion regulation. Regression analyses showed that lower parenting sensitivity at bedtime was associated with lower executive functioning and more labile and less adaptive emotion regulation only for children who showed less cortisol decline from morning to evening, suggesting that adaptive cortisol patterning may be protective in the context of low parenting sensitivity. The findings identify children at greatest risk and inform interventions targeting children's developmental outcomes.