Two studies determined whether interval exercise reduces children's stress reactivity. For Experiment 1 children completed interval exercise (n=14) or watched TV (n=14) for 25 min. After 20 min rest children completed a speech task. Speech-induced diastolic blood pressure (DBP) reactivity was dampened in the exercise group (p<.05). For Experiment 2 children (n=22) completed interval exercise-speech and TV-speech conditions on separate days. Physical activity was assessed by accelerometry and aerobic fitness estimated by submaximal exercise. DBP, systolic BP, and heart rate (HR) reactivity to the speech stressor were dampened (p<.05) after exercise compared to TV watching. Fitness was positively associated with HR reactivity. Interval exercise that mimics usual patterns of physically active play dampens cardiovascular reactivity to interpersonal stress.