Abstract
Based on an analysis of natural production data, I show that Italian children, at a young age, distinguish between finite and infinitival verbs. The evidence comes from the distribution of these two classes of verbs and from the placement of clitic (atonic) pronouns. I argue that, from the earliest stages, Italian children have knowledge of the verbal agreement system, a claim supported by a quantitative analysis of the verbal agreement paradigm. These results—evaluated in the framework of 'the principles and parameters theory of grammar—are naturally interpreted as evidence that the initial structure of children's sentences includes functional categories, specifically the Inflectional Phrase.