This study aims to set a cooperative network system for children's service in public libraries in Korea centering on the National Library for Children and Young Adults. The purpose of the study is to foster effective online and offline cooperation among public libraries through the National Library for Children and Young Adults and improve children's library service. Based on the survey results and face-to-face interviews the study suggests various ways to strengthen cooperative network system and public library council for children's service. First is to empower the council and to that end, to expand the cooperative network as well as to clearly set its role. Secondly it advises to capitalize from council's homepage service and adapt social-networking tools.