Children use similarity, propinquity, and loyalty to predict which people are friends

Friendship fundamentally shapes interactions, and predicting other people's affiliations is crucial for effectively navigating the social world. We investigated how 3- to 11-year-old children use three cues to reason about friendship: propinquity, similarity, and loyalty. In past work, researchers asked children to report on their own friendships and found a shift from an early focus on propinquity to a much later understanding of the importance of loyalty. Indeed, attention to loyalty was not standard until adolescence. Across four studies (total N = 900), we used a simpler method in which we asked children to make a forced-choice decision about which of two people a main character was better friends with. Although we replicated the finding that understanding the importance of loyalty increases with age, we also found evidence that even the youngest children tested (3- to 5-year-olds) can use loyalty to predict friendship. Thus, a sophisticated understanding of how social interactions unfold differently between friends and nonfriends may be evident by the preschool years. We also discuss interesting developmental differences in how children weigh the importance of each of these friendship cues.