Language mixing is common in bilingual children's learning environments. Here, we investigated effects of language mixing on children's learning of new words. We tested two groups of 3-year-old bilinguals: French–English (Experiment 1) and Spanish–English (Experiment 2). Children were taught two novel words, one in single-language sentences (“Look! Do you see the dog on the teelo?”) and one in mixed-language sentences with a mid-sentence language switch (“Look! Do you see the chien/perro on the walem?”). During the learning phase, children correctly identified novel targets when hearing both single-language and mixed-language sentences. However, at test, French–English bilinguals did not successfully recognize the word encountered in mixed-language sentences. Spanish–English bilinguals failed to recognize either word, which underscores the importance of examining multiple bilingual populations. This research suggests that language mixing may sometimes hinder children's encoding of novel words that occur downstream, but leaves open several possible underlying mechanisms.

Hearing words in sentences facilitates word recognition in monolingual children. Many children grow up receiving input in multiple languages – including exposure to sentences that ‘mix’ the languages. We explored Spanish–English bilingual toddlers’ (n = 24) ability to identify familiar words in three conditions: (i) single word (ball!); (ii) same-language sentence (Where's the ball?); or (iii) mixed-language sentence (Dónde está la ball?). Children successfully identified words across conditions; however, the advantage linked to hearing words in sentences was present only in the same-language condition. This work hence suggests that language mixing plays an important role on bilingual children's ability to recognize spoken words.