Children raised in the home as English or Welsh monolinguals or English-Welsh bilinguals were tested on untrained word form recognition using both behavioral and neurophysiological procedures. Behavioral measures confirmed the onset of a familiarity effect at 11 months in English but failed to identify it in monolingual Welsh infants between 9 and 12 months. In the neurophysiological procedure the familiarity effect was detected as early as 10 months in English but did not reach significance in monolingual Welsh. Bilingual children showed word form familiarity effects by 11 months in both languages and also revealed an online time course for word recognition that combined effects found for monolingual English and Welsh. To account for the findings, accentual, grammatical, and sociolinguistic differences between English and Welsh are considered.