We explored whether bilingual toddlers make use of semantic and phonological overlap between their languages to learn new words. We analysed cross-sectional and longitudinal CDI data on the words understood and produced by 1.0 to 3.0-year-old bilingual toddlers with English and one additional language. Cognates were more likely to be understood and produced compared to non-cognates. Cognate effects were modulated by whether the toddler knew the translation equivalent in the other language, highlighting that young learners are sensitive to the similarities across their languages. Additionally, exploratory analyses suggest that children with smaller vocabularies rely more on translation equivalents to support the acquisition of difficult words. Children with larger vocabulary sizes exhibited no preference for translation equivalents in comprehension, and a preference for new concepts in production. The rapid acceleration of vocabulary growth in the second year of life may explain this developmental change in translation equivalent preference.

Bilinguals need to learn two words for most concepts. These words are called translation equivalents, and those that also sound similar (e.g., banana–banane) are called cognates. Research has consistently shown that children and adults process and name cognates more easily than non-cognates. The present study explored if there is such an advantage for cognate production in bilinguals’ early vocabulary development. Longitudinal expressive vocabulary data were collected from 47 English–French bilinguals starting at 16–20 months up to 27 months (a total of 219 monthly administrations in both English and French). Children produced a greater proportion of cognates than non-cognates, and the interval between producing a word and its translation equivalent was about 10–15 days shorter for cognates than for non-cognates. The findings suggest that cognate learning is facilitated in early bilingual vocabulary development, such that phonological overlap supports bilinguals in learning phonologically similar words across their two languages.

Most English compounds are spaced compounds, whereas spelling regulations prescribe Finnish compounds to be written in a concatenated format. However, as in English, Finnish compounds are commonly spaced nowadays (e.g., piha juhla ‘garden party’), a phenomenon that we labeled the ‘English disease’. In this eye movement study with Finnish–English bilinguals we investigate whether the reading of a concatenated or illegally spaced Finnish compound is affected by the spelling of an English translation equivalent (ETE). We found that spaced Finnish compounds were read slower than their concatenated counterparts, but this effect was attenuated when ETEs were thought to be spaced. Similarly, concatenated Finnish compounds were read faster when their ETEs were also concatenated. These backward transfer effects are in line with studies that show that processing behavior in L1 is affected by a strong concurrent L2, even when the L1 is the native language as well as the dominant community language.

The present study investigated the impact of translation equivalents (TE) on lexical processing in a sample of 36 French–English bilingual toddlers at 22-months of age. Children were administered the Computerized Comprehension Task (CCT; Friend & Keplinger, 2003) in each language and parents completed the MacArthur Bates Communicative Development Inventory (CDI) in both English and French across two visits (one language per visit). Correct trials on the CCT were identified and classified into one of two categories: words with a known TE as reported on the CDI and words without a known TE on the CDI. Reaction times for correct trials were averaged and compared for each of the bilinguals’ languages. Interestingly, children were faster to retrieve words with a known TE on the CDI than words with no known TE. The present findings suggest that the translation facilitation effects reported in adult bilinguals are also present in very young bilinguals.