Children infer speaker groups from variation in morphosyntactic patterns.

Variation in how people use language provides powerful cues to social identity. As children join a language community, they must acquire such sociolinguistic knowledge. Prior work shows that children link broad language varieties to social groups, but little is known about whether they can use variation in specific language features to infer speakers' group membership. 40 English-speaking children aged 5-6 years (M = 72.2 months; Nfemale = 22, Nmale = 18; NWhite = 35, NAsian,White = 3, NBlack,White = 1; Nother = 1; all non-Hispanic) participated between October 2024 and August 2025 in a semi-artificial language learning study in which they were exposed to 2 alien groups that differed in plural marking. Children were then tested on their ability to determine which group new aliens belong to based solely on their plural usage. Children succeeded when the group-marker mappings were deterministic, but not when they were probabilistic. These findings suggest that young children use consistent morphosyntactic patterns to infer group membership and highlight a novel approach to studying sociolinguistic learning. Future research will extend this paradigm to include more realistic social categories that are meaningful to children.