International audience This study investigates the impact of the input in language acquisition of young bilinguals (5-7 y.) from mixed French- and Russian-speaking families living in France. The results of our previous research on fluency in bilingual children’s speech productions showed the importance of the input: the French dominated in bilinguals going to French schools and children with more Russian input had a better fluency score in Russian (Tiulkova, 2017). Active and passive lexical knowledge was tested through a picture-naming task (Gagarina et al., 2015) and oral production was elicited by means of an original picture-story retelling task (similar to Mayer, 1969). Moreover, the sociolinguistic profiles of families were also taken into account, so we could compare the data obtained in 2 different configurations: Bilingual First Language Acquisition, and Early Second Language Acquisition (Caroll, 2017 ; De Houwer, 2017). However, only L2 oral fluency measures such as speed, breakdown, repair and composite fluency (De Jong et al., 2013; Skehan, 2003; Tavakoli, 2016) were examined. Thus, the present work focuses on the quality and quantity factors of the input, a speech that children hear (De Houwer, 2009), and involves the analysis of child speech productions in connection with parents’ interactions and language questionnaires (Duguine et al., 2014). Furthermore, the simultaneous bilingual language development study requires an access to the longitudinal data (ie, constitution of our future corpus FRUBIC: French-Russian Bilingual Children Corpus).