Objective: The purpose of this study was to examine the effects of fathers’ playfulness on their children’s social competence and emotional regulation, and the moderating effects of the fathers’ play participation level on the relationship between his playfulness and his child’s social competence and emotional regulation. Methods: The participants in this study were 139 children and their fathers. The children were aged between four and five years old attending nine preschools in Seoul. The collected data was analyzed through Pearson’s correlations, and hierarchical regression analysis using SPSS 21.0. Results: First, fun-loving fathers had a significant effect on the cooperation and sociability of their children. Second, fun-loving fathers had a significant effect on their children’s emotional regulation. Third, fathers’ play participation level moderated the relationship between them enjoying silliness and their children’s sociability. Fourth, fathers’ play participation level moderated the relationship between them being fun-loving and their children’s emotional regulation. Conclusion/Implications: The results of this study address the need for a high level of fathers’ play participation in relation to the development of their children’s social competence and emotional regulation.