Aims: The present study aims to examine: (1) the relationship between young children’s bilingualism and their performance in the Dimensional Card Change Sort (DCCS) task; and (2) whether prefrontal activation was associated with children’s bilingualism and executive function. Methodology: Children performed three sessions of the DCCS and their brain activity during the task was measured using functional nearinfrared spectroscopy (fNIRS). Data and analysis: A sample of bilingual children (N = 49) was recruited from a preschool with an English immersion program. We examined whether children’s performance in the DCCS was related to their bilingualism and whether the changes in oxygenated hemoglobin in the prefrontal regions were related to their bilingualism and performance in the DCCS. Findings/conclusions: Results showed that children’s English ability was significantly correlated with their behavioral performance in DCCS, and predicted children’s group membership (pass or perseverate). Furthermore, children in the pass group significantly activated the prefrontal cortex than those in the perseverate group, and activation in the prefrontal region was significantly correlated with children’s English ability. Originality: The current study first examined the effect of children’s bilingualism on their executive function and prefrontal activation.