Objectives: The purpose of this study was to investigate the differences of children’s diurnal cortisol change in childcare according to temperament, peer relationship, teacher-child relationship with a specific focus on the differences according to childcare duration.

Methods: The participants included 60 three-year-olds attending to one of nine childcare centers located in Daejeon and Daegu, South Korea. The children participated in saliva sample collection for two days, around 10 a.m. and 3 p.m. The parents assessed their children’s temperament via a questionnaire. The teachers assessed the children’s peer relationship and teacher-child relationship via a questionnaire. Data were analyzed using Analysis of Variance (ANOVA).

Results: Among children who had attended childcare for less than a year, higher levels of surgency or inhibitory control were related to an increased rise in cortisol in the afternoon. In the group of children that had been in childcare for more than a year, closer relationships with peers and teachers were tied to a smaller afternoon cortisol rise.

Conclusion: The findings illustrate the complex nature of physiological adjustment for children in childcare. The relationship between temperament, peer relationship, teacher-child relationship and diurnal change of cortisol was found in longer childcare durations.