For socially appropriate communication, speakers must command a variety of linguistic styles, or "registers", that vary according to social context and social relationships. This study examined preschool children's ability to use a speaker's register choice to infer the identity of their addressee. Four-year-olds could draw correct inferences based on Spanish and formal speech, and had limited success with infant-directed and casual styles. Five-year-olds drew appropriate inferences with all 4 styles; moreover, these children demonstrated strong explicit understanding of register, as measured through response justifications. These results demonstrate that children can use language for social judgments that extend beyond evaluating the speaker, and can interpret social implications of language even when not directly engaged in the particular social interaction.