Children with elevated behavioral inhibition (BI) show context-inappropriate fear and dysregulated RSA across stressor tasks. However, few studies have examined dynamic RSA within tasks and relations to parent and child anxiety. Using piecewise growth modeling and multi-method baseline data from an intervention study of 151 3.5-5 year old children and their parents, the individual and interactive influences of child social anxiety (SA) and parent anxiety (via diagnostic interviews) in predicting children’s RSA across social stressor tasks (e.g.,learning about unfamiliar peers, Trier Social Stress) were tested. Children high in SA showed RSA responses indicative of avoidant coping, whereas those low in SA showed responses suggesting attention in anticipation of meeting unfamiliar peers. The relation between child SA and RSA across tasks was moderated by parent anxiety, specifically for dyads matched in anxiety. Findings provide support for the influence of both child and parent anxiety on children’s RSA response across specific stressor and non-stressor tasks.