Abstract: In this study, Cardiac vagal tone and heart period were measured in a sample of 104 children (aged 2, 4, and 6) to evaluate the development of vagal regulation at rest and during age-appropriate mild stress task. The development patterns of child baseline vagal tone and child vagal suppression were different: (1) Child baseline vagal tone increased with age in early childhood. The baseline vagal tone of 4 years and 6 years were significantly higher than that of 2 years, but there was no significant difference between that of 4 years and 6 years. Child baseline heart period increased with age. (2) Child vagal suppression didn’t increase with age. Child baseline-to-task change in heart period of 6 years was significantly higher than that of 2 years, and there were no differences between those of other groups

Key words: cardiac vagal tone, baseline vagal tone, vagal suppression