This study examines the syntactic and semantic factors in children’s initial production of determiners. Using longitudinal corpora of two monolingual Spanish-speaking children, we investigate whether children exhibit sensitivity to the pre-/post-verbal asymmetry, and awareness of the count-singular, mass and count-plural distinction from an early age. Our results indicate that the children in this study have determiners from a very young age, but their initial use is not as generalized as adults’. The data suggest that the different quantitative status of the relevant input across domains and categories (lexical class, number, function and position) plays a role in development. We conclude that children attend to the categorical distinctions, rather than the overall variability in the input, in the process of acquiring the determiner system.