This study explored the effects of quantity and quality of input on bilingual children's acquisition of complex plural morphology in Welsh. Study 1 explored the quality of adult input and revealed target-like marking of plural forms in naturalistic adult speech. Study 2 presented eighty-eight 7–11-year-old children, across three bilingual language groups (L1 Welsh, 2L1, and L2 Welsh), with a plural production task. Results revealed performances approaching L1 adult norms among L1 Welsh-speaking bilinguals, but delayed progression among 2L1 and L2 Welsh bilinguals, although analyses of errors revealed various levels of structural knowledge. Forms requiring the addition of a plural suffix were less difficult to acquire than those involving alterations to the root, with each type acquired with greater levels of accuracy with increasing levels of exposure to the language. The implications of these findings for our understanding of bilingual acquisition of complex structures under minority language conditions are discussed.