Bilingual language development might be characterized by transfer, deceleration,and/or acceleration, the first two being relevant for the language impairmentdiagnosis. Studies on bilingual children’s productive phonology showevidence of transfer, but little is known about deceleration in this population.Here, we focused on phonological transfer and deceleration in L1 speech oftypically developing Polish-English bilingual children of Polish migrants to theUnited Kingdom (aged 4.7–7). We analyzed L1 speech samples of 30bilinguals and 2 groups of Polish monolinguals, matched to the bilinguals on ageor vocabulary size. We found that bilingual children’ speech (bothsimultaneous and early sequential) was characterized by transfer, but not bydeceleration, suggesting that while phonological deceleration phases out inchildren above the age of 4.7, transfer does not. We discuss our findings withinthe PRIMIR model of bilingual phonological acquisition (Curtin et al., 2011) andshow their implications for SLT practices.