Bilingual and monolingual children's (mean age = 4;10) elicited production of the past tense in both English and French was examined in order to test predictions from Usage-Based theory regarding the sensitivity of children's acquisition rates to input factors such as variation in exposure time and the type/token frequency of morphosyntactic structures. Both bilingual and monolingual children were less accurate with irregular than regular past tense forms in both languages. Bilingual children, as a group, were less accurate than monolinguals with the English regular and irregular past tense, and with the French irregular past tense, but not with the French regular past tense. However, bilingual children were as accurate as monolinguals with the past tense in their language of greater exposure, except for English irregular verbs. It is argued that these results support the view that children's acquisition rates are sensitive to input factors, but with some qualifications.