We study the acquisition of abstract syntactic categories of words in children by using a computational model of categorization. Especially, we examine the effect of word-internal properties, such as morphological and phonological cues, on the identification of different categories, such as nouns, verbs, and determiners. To evaluate our model, we use it to determine the syntactic category of actual novel words selected from naturalistic child-directed utterances. We argue that such an evaluation is necessary for a better understanding of the effect of different cues (including word-internal properties and contextual cues) on category acquisition.