Three or four-year old children who spend a lot of time together, as happens in a kindergarten, may ‘get infected’ by certain traits their friends have. Children whose play mates are outgoing or work hard tend to copy these traits in time. Instead, children whose friends are anxious or easily discouraged do not copy these behaviors. The test that decides if a certain trait will undergo contagion is playing together. Features that contribute to the success of the game will be copied (outgoing, working hard), whereas features that negatively affect the game will not be imitated (anxiety, discouragement). Kids benefit from going to kindergarten and kindergartens must be designed and built as places where kids have the opportunity to play.