Language proficiency before school entry has proven to be a powerful predictor of literacy development. This longitudinal study examined how simultaneous exposure to two richly inflected languages from birth contributes to the development of language-related literacy precursors at preschool age compared to peers exposed to one language. The community language turned out to be the stronger language of the bilinguals by 4 years of age and to a great extent age-appropriate compared to monolingual peers. The same initial exposure conditions resulted in three bilingual and two monolingual language proficiency profiles. For the bilinguals changes in the proportion of exposure to two home languages and frequency of language-specific social interactions explained proficiency in each language, whereas for the monolinguals exposure did not explain language proficiency. Our findings give support for the primary impact of exposure on the development of bilingualism and preliteracy skills.