Language development in bilingual children is often related to differing levels of proficiency. Objective measurements of bilingual development include for example mean length of utterance (MLU). MLU is almost always calculated for each language context (including both monolingual and code-mixed utterances). The current study analyzed the MLUs of three German-English bilingual children, aged 2;3–3;11 separately for the monolingual and code-mixed utterances. The results showed that language preference was reflected in MLU values: the more children spoke in one language the higher the MLU was in that language. However, it was the mixed utterances that had the highest MLU for all three children. The study supports the results with a construction type analysis and suggests a potential usage-based explanation for these results based on individual differences in each child’s developmental inventory of words and constructions. Keywords: code-mixing, MLU, language proficiency, German – English, bilingual child