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Many children worldwide grow up hearing multiple languages, and thus learn vocabulary words in each. How does the number of languages being learned affect multilinguals’ vocabulary development? In a pre-registered study, we compared productive vocabularies of bilingual (n = 170) and trilingual (n = 20) toddlers aged 17–33 months growing up in a bilingual community where both French and English are spoken. We hypothesized that because trilinguals have reduced input in French and English due to time spent hearing their third language, they would have smaller French–English vocabulary sizes than bilinguals. Trilinguals produced on average 2/3 of the number of words in these languages that bilinguals did, in line with theories that emphasize the role of input quantity on vocabulary acquisition. Younger children and boys also had smaller vocabularies. Together, our results indicate that similar factors contribute to vocabulary development across toddlers regardless of the number of languages being acquired.