This study examined the moderating role of child effortful control on the association between observed parental hostility and parents' cortisol awakening response (CAR), a critical index of stress system functioning. Participants included 99 medication-free parents and their preschool-aged children. Parents obtained salivary cortisol samples at waking, 30, and 45 minutes post-waking and at bedtime across two consecutive days. Parental hostility was assessed during an observational parent-child interaction task, and child effortful control was assessed using parent report.

Observed parental hostility was associated with parents' lower cortisol levels at 30 and 45 minutes post-waking and lower CAR. Low levels of child effortful control were associated with parents' lower bedtime cortisol. Moreover, results demonstrated an interaction effect between parenting and child behavior on parent CAR. The findings highlight the significance of continued examination of the neurobiology of parenting with a focus on the interactive effects between parenting and child behavior.