In two sentence repetition experiments, we investigated whether four- and five-year-olds master distinct representations for intransitive verb classes by testing two syntactic analyses of unaccusatives (Burzio, 1986; Belletti, 1988). Under the assumption that, with unaccusatives, the partitive case of the postverbal argument is realized only on indefinites (Belletti, 1988), we tested whether children used indefiniteness as a feature to assign the partitive case to the verb's argument. In the sentences, we manipulated whether the subject preceded or followed the (unaccusative or unergative) verb and whether the subject was expressed by means of a definite or indefinite NP. With unaccusatives, children tended to place the subject in the postverbal position when the subject NP was indefinite, whereas, when the sentence presented a definite postverbal subject, children preferred to place the definite subject in the preverbal position. Definiteness exerted an effect only with unaccusatives, suggesting that children treated unergatives and unaccusatives differently.