Increasing evidence from behavior and neuroimaging research indicates that executive function (EF) is related to creativity. However, most of these studies focused on adult and adolescent populations. The relationship between EF and creativity is unknown when EF undergoes rapid development during early childhood, due to the preschoolers' marginal skills of expressing their ideas, orally or in writing. Using a nonverbal, open-ended test, the present study examined whether creative thinking was related to cognitive flexibility in young children. Preschool children (N = 26) performed the Dimensional Change Card Sort (DCCS) and the Unusual Box Test (UBT), while their brain activation was recorded using functional near-infrared spectroscopy (fNIRS). We did not find any significant correlation between children's cognitive flexibility and creative thinking. However, fNIRS analyses showed that children's brain activation in the lateral prefrontal regions was significantly greater during the test phases of the UBT. Additionally, children who strongly recruited their ventrolateral prefrontal regions during the post-switch phases of the DCCS recruited the same regions while performing the UBT. Taken together, these findings suggest that children recruit their lateral prefrontal regions when expressing creative thinking, and that such creative thinking could be partially supported by cognitive flexibility in early childhood.