Monolingual children tend to assume that a word labels only one object, and this mutual exclusivity supports referent selection and retention of novel words. Bilingual children accept two labels for an object (lexical overlap) for referent selection more than monolingual children, but in these previous studies, information about speakers’ language backgrounds was minimal. We investigated monolingual and bilingual 4-year-old children’s ability to apply mutual exclusivity and lexical overlap flexibly when objects were labelled either by one or two speakers with the same or different language backgrounds. We tested referent selection and retention of word–object mappings. Both language groups performed similarly for mutual exclusivity, were more likely to accept lexical overlap in the two-language than one-language condition, and performance was similar for referent selection and later retention. Monolingual and bilingual children can adapt their word-learning strategies to cope with the demands of different linguistic contexts.

This study piloted CHIPUTIL, an automated tool in CLAN for analysing sequential lexical overlap in parent–child conversations. In a sample of 44 dyads (child age M = 1;9), child spontaneous lexical overlap was positively associated with parent imitations and expansions, across the conversation and within sequential turns. Children were more than twice as likely to respond with lexical overlap when parents first produced an imitation or expansion. These findings offer insight into how lexical overlap may unfold in early conversations. We discuss implications of automated coding and future directions in exploring the role of lexical overlap in children’s language development.

Mutual Exclusivity (ME) is a prominent constraint in language acquisition, which guides children to establish one-to-one mappings between words and referents. But how does unfolding experience of multiple-to-one word-meaning mappings in bilingual children's environment affect their understanding of when to use ME and when to accept lexical overlap? Three-to-five-year-old monolingual and simultaneous bilingual children completed two pragmatically distinct tasks, where successful word learning relied on either the default use of ME or the ability to accept overlapping labels. All children could flexibly use ME by following the social-pragmatic directions available in each task. However, linguistic experience shaped the development of ME use, whereby older monolinguals showed a greater reliance on the one-to-one mapping assumption, but older bilinguals showed a greater ability to accept lexical overlap. We suggest that flexible use of ME is thus shaped by pragmatic information present in each communicative interaction and children's individual linguistic experience.