We investigated the speech patterns and accentedness of Polish–English bilingual children raised in Great Britain to verify whether their L1 Polish would be perceived as different from that of monolinguals matched for age and socioeconomic status. To this end, Polish-language speech samples of 32 bilinguals and 10 monolinguals (a 3:1 ratio, MAge = 5.79) were phonetically analysed by trained phoneticians and rated by 55 Polish raters, who assessed the degree of native accent, intelligibility, acceptability and perceived age. The results show significant differences in the phonetic performance of bilingual and monolingual children – both in terms of atypical speech patterns uncovered in the phonetic analysis and in terms of the holistic accentedness ratings. We also explored the socio-linguistic predictors of accent ratings in bilingual speech and found that the amount of L1 Polish input was the main predictor of accentedness in children's L1 Polish speech, while L2 English input was marginally significant. (149)