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