\n This study analysed longitudinal data from eight Cantonese-English bilingual children in the Hong Kong Bilingual Child Language Corpus. It discussed two types of code-mixing: intra-utterance and inter-utterance mixing. Intra-utterance mixing refers to a combination of elements of both languages within the same utterance, while inter-utterance mixing here refers to the child’s producing one language in a context where the other language would be appropriate. \nThis study found that language dominance was a motivational factor to explain the children’s inter-utterance mixing. It was found that when the children were in the conversational context of their non-dominant (or weaker) language, they would have a tendency to resort to their dominant (or stronger) language, resulting in inter-utterance code-mixing. On the other hand, language dominance was not found to be a motivational factor for their intra-utterance mixing. Petersen’s (1988) Dominant Language Hypothesis was tested on two of the children, and their results did not comply with the predictions of the Hypothesis. \nThis study found that the theory of “language socialisation” provided a better explanation for the children’s intra-utterance mixing. It was proposed the children were gradually socialised into the community patterns of intra-utterance code-mixing over the years of language acquisition. The Matrix Language Frame model was adopted to decode those syntactic patterns, and make comparison with Hong Kong adults’ code-mixing. Other explanations such as lexical gap and pragmatic factors were also discussed. \nMuch of the previous research on Hong Kong bilingual children’s code-mixing has focused on the intra-utterance kind, and little has been done on their inter-utterance mixing. Hopefully, this study will inspire further discussion in the academia regarding the different forms of code-mixing and their psychological and social implications.