There is lack of agreement among world researchers in regards to the extent of differences between the phonological development of monolingual and bilingual children. While some research provides evidence for the lack of significant differences, other studies indicate that bilingual children make phonological errors which might be considered atypical of their monolingual counterparts. If indeed bilingual children follow a unique path in their phonological development, it is important to investigate this path in order to facilitate accurate phonological diagnosis of bilingual children by speech pathologists. The present research, conducted with a group of ten pre-school and early schoolage English-Polish bilingual children in Australia, describes and compares the phonological patterns present in the speech of typically-developing children, when they speak English and Polish. Popular tests used by speech pathologists have demonstrated that the children have two separate but mutually dependent phonological systems, which are different from the systems of their monolingual peers. The research has noted a number of cross-linguistic errors, especially from English, that is the dominant language for the participants. Some of the phonological patterns identified in the study, although atypical of monolingual children, could be typical of English-Polish bilinguals. Knowledge about such patterns may facilitate accurate diagnosis of English-Polish bilingual children in Australia or in Poland if their parents decide to re-emigrate.