This study examined the influence of linguistic input on the development of productive and receptive skills across three fundamental language domains: lexico-semantics, syntax, and phonology. Seventy-one (35 female) Basque-Spanish bilingual children were assessed at three time points (Fall 2018, Summer 2019, Winter 2021), between 4 and 6 years of age, by specifically examining language knowledge and spontaneous language use in each language. A direct impact of the amount of linguistic exposure on the longitudinal growth of lexico-semantic and syntactic abilities was observed in both languages. While phonological skills were not directly influenced by exposure, they were more proficient in the more exposed language. The use of lexically diverse and syntactically rich utterances developed relatively later than language knowledge, both supported by the amount of linguistic exposure.