<p>A substantial number of existing studies have explored the characteristics of intergroup attitudes in adults. However, there is no consensus on when children show intergroup attitudes. In the present study, we explored the intergroup attitudes of 75 preschool-aged children (aged 3–5 years) using the minimal group paradigm and resource allocation task. The results showed no significant difference in the number of stars assigned to in-group and out-group members by 3-year-old children. In contrast, 4-year-old children manifested such differences, assigning more stars to in-group members. This trend intensified among 5-year-old children, who allocated even more stars to in-group members. These results suggest that children’s preference for their in-group emerges at around the age of 4 and becomes more pronounced with age. The results meaningfully explain the timing of occurrence of children’s intergroup attitudes and proffer theoretically grounded recommendations and evidence-based strategies for fostering positive intergroup attitudes during the early childhood developmental stage.</p>