First Sounds, Second Language: How Word Onsets Spark Language Co‐Activation in 3‐Year‐Old Bilinguals

Adult and young bilinguals co‐activate their languages to different degrees, even in entirely monolingual tasks. However, many studies use translation pairs with high phonological overlap (e.g., the English‐GERMAN: “milk”‐“MILCH”), making it difficult to discern the origin of the co‐activation. This study examined language co‐activation in Catalan‐Spanish bilingual toddlers using words with minimal phonological overlap across translations. Thirty Catalan‐Spanish bilingual three‐year‐olds ( N = 30; M age = 36.38 months, range = 35.57–37.43) participated in a visual word paradigm conducted entirely in Catalan, searching for an absent target named in Catalan (e.g., “apple” in Catalan: “ p oma ,” Spanish: “ M ANZANA”) among images with labels that shared the initial phoneme across languages or were unrelated. The design included three types of images: (a) direct phonologically related (e.g., Spanish “ P ATO” for “duck”), (b) indirect phonologically related (e.g., Catalan “ m itjó ” for “sock”), and (c) unrelated (e.g., “brush,” “sandwich”). If bilingual toddlers co‐activate languages, they should look more at phonologically related than unrelated images due to shared phonological onsets. The results supported the hypotheses and provided solid evidence that young bilinguals co‐activate phonologically related words in their familiar languages. Moreover, contrasting direct and indirect (translation‐mediated) competitors showed that language co‐activation unfolds dynamically, with timing shaped by the number of links involved.