Although thoroughly analysed in adult second language acquisition (L2A), the acquisition of subject properties in child L2A has not received so much attention and the majority of studies deal with longitudinal data or only with a single subject property. This study contributes new cross-sectional data from 5-year-old Spanish children acquiring second language (L2) English in an immersion bilingual context with age of onset three and analyses the acquisition of all the subject properties traditionally associated as a cluster in comparison to a monolingual control group of the same age. The data were obtained by means of an orally elicited judgement/correction experimental task and enabled us to explore the children's awareness of grammaticality contrasts in their L2, the influence of their L1 after two years of exposure and the extent to which the cluster of subject properties traditionally associated and studied together develop similarly in acquisitional terms. Results suggest that 5-year-old children show sensitivity to grammaticality contrasts in their L2 English and indicate that even after two years of exposure and although the age of onset of acquisition was only three, their L2 is influenced by their first language (L1) subject properties, although developmental effects also need to be taken into account when explaining the results. (Contains 5 tables, 1 figure, and 9 notes.)