The present study examined associations between both children’s physiological regulation capacity and regulation when discussing disappointing a parent and children’s trait-like adaptive and maladaptive guilt. High-frequency heart rate variability (HF-HRV) was calculated from electrocardiograms of children (N = 104, Age Mean = 9.12, SD = 1.10 years) at rest (regulation capacity) and during the parent-child disappointed discussion. Children’s trait-like maladaptive (child-report) and adaptive (parent-report) guilt were measured with behavioral rating scales. Children’s regulation capacity was unrelated to guilt. Children’s discussion regulation had a significant negative accelerating quadratic relationship with children’s maladaptive guilt wherein for children with below average HF-HRV there was no significant association between HF-HRV and guilt, and for children with above average HF-HRV higher levels of HF-HRV were associated with lower maladaptive guilt. Children with high regulated engagement may have lower levels of maladaptive guilt as they can flexibly engage with others’ emotions without becoming over-aroused or withdrawing.