Written from a social interaction perspective, this digest provides an overview of children's language development in the first five years of life. Viewing language learning as both a social and a developmental process, the digest's three sections outline the process of language development in the first year, the second and third year, and in the preschool years. It argues that, to acquire a language, children must interact with other more competent language users as well as explore various aspects of the linguistic system. It concludes that during the early years of language learning, children also create, test, and revise their hypotheses regarding the use of language. (Contains 13 references.) (SR)