"You didn't take my side!": When children expect others to be more upset at friends.

Loyalty is a defining feature of adult friendships, but when does it become key to children's friendships? In three studies (N = 429), we assessed children's beliefs about loyalty among friends. In Study 1, 4- to 11-year-olds were told that a protagonist stayed out of (i.e., remained neutral to) a situation involving their friend and acquaintance and were asked who they thought would be more upset at this. As children matured, they were more likely to predict that the protagonist's friend would be more upset than the protagonist's acquaintance at their neutrality. Study 2 replicated this finding in 4- to 11-year-olds and tested a boundary condition of our account in which we predicted and found that children did not believe a friend would be more upset than the protagonist's acquaintance, namely, when friends made mistakes. Study 3 tested whether 6- to 7-year-olds and 10- to 11-year-olds can use upset reactions to infer friendship. We found that 10- to 11-year-olds inferred that a person who was upset at the protagonist's neutrality was the protagonist's friend but thought that a person who was upset at the protagonist's mistake was not their friend. However, 6- to 7-year-olds were less likely to infer that the upset person was the friend in the neutrality context and responded similarly in both conditions. Altogether, children increasingly expected friends to be upset at disloyalty from their friends as they matured. We interpret these findings as evidence for a developing belief about the loyalty obligations that exist in friendships. (PsycInfo Database Record (c) 2026 APA, all rights reserved).