Objective: The purpose of this study was to develop a sociability program for young children (Buddy TOC), consisting of cooperative activities, and to investigate its effects on children's sociability, such as empathy, self-regulation, and interpersonal skills. Methods: The contents of the program were extracted through a literature review and analysis of previous research. The goodness-of-fit of the drafted program was verified by specialists in early childhood education and through a preliminary study. The effects of 'Buddy TOC' were tested based on the selected 5 sessions with regard to children's empathy, self-regulation, and interpersonal skills. Overall, 70 participants (35 in the experimental group and 35 in the comparison group) were 4-year-olds, and 67 participants (33 in the experimental group and 34 in the comparison group) were 5-year-olds. The data were analyzed by conducting ANCOVA based on age. Results: Empathy, self-regulation and interpersonal skill of the 4- and 5-year-old children in the experimental group were higher than those of the comparison group, and there were slight differences according to the subareas. Conclusion/Implications: The field applicability and importance of 'Buddy TOC' as a sociability program, utilizing cooperative activities for the promotion of young children's social skills, were discussed.