The present study compares (1) monolingual English vs. French adults and children and (2) simultaneous French-English bilingual children who describe caused motion events. The results concerning L1 speakers showed developmental progressions in both languages, e.g., utterance complexity increases with age. However, response patterns differed considerably across languages in that responses were ... [Show full abstract] denser and more compact in English than in French. The results concerning bilingual children showed unidirectional crosslinguistic interactions. Responses elicited in English paralleled monolingual developmental patterns, whereas bilinguals’ French productions differed from those of monolingual French peers. The findings suggest that bilingual children transfer lexicalisation patterns from one of their languages to the other when the former provides more transparent means of achieving high semantic density.