Hint: It has to do with confidence. 

Children running in a field
Credit: Stephanie Rausser

By the time your kids head off to school—kindergarten even—their self-esteem might already be fully developed and like that of an adult, suggests a new study from The University of Washington.

The research, published in the January 2016 issue of the Journal of Experimental Social Psychology, used a newly developed test to assess the self-esteem of more than two-hundred 5-year-old children from the Seattle area (the youngest age studied to date). To measure children's positive feelings about themselves, the researchers used a tool called the Preschool Implicit Association Test (PSIAT). When taking the PSIAT, kids categorized "good" words (like fun and happy) and "bad" words (think: mad and mean) as "me" or "not me." Overall, both boys and girls associated themselves with more positive words.

"Previously we understood that preschoolers knew about some of their specific good features. We now understand that, in addition, they have a global, overall knowledge of their goodness as a person," study co-author Anthony Greenwald said in a statement. ​​"It is a social mindset children bring to school with them, not something they develop in school,"​ ​adds Andrew Meltzoff, study co-author and co-director of I-LABS.

To further understand a child's sense of self, the researchers conducted two additional tests that examined the study participants' gender identity and whether that child preferred to associate with other kids of his or her own gender. According to the results of these two tests, children who had high self-esteem and strong gender identity also showed stronger preferences for members of their own gender.

These findings suggest kids' self esteem develops at an unexpectedly young age, plays a critical role in how children form various social identities, and underscores the importance of the first five years as a foundation for life​, said Cvencek. "What aspects of parent-child interaction promote and nurture preschool self-esteem? That's the essential question. We hope we can find out by studying even younger children," said Meltzoff.​