The purpose of this study was to suggest the collection codes and simplification of call numbers for children's easy access to the children's materials. The classification schemes, author tables, expansion of classification schemes, collections codes, classification numbers used in domestic and foreign children's libraries were surveyed through questionnaires and interviewing with librarians. As a result, in foreign children's libraries, it was common practice to shelve children's materials separately into various collections and sub-collections, to mark the spine with collection code and the lead characters of the author's last name, and not to stick with their classification scheme when it comes to highly circulated children's materials such as fiction, picture book, biographies and so on. Also, in domestic children's libraries, it was found that a collection code was used a few and each call number was almost assigned by KDC number. Therefore, it was suggested that the types and codes of collection and sub-collection were divided as non-fiction, fiction, fiction/mystery, fiction/science fiction, picture book, cartoon, language, folks and fairy tales, biographies, legend, concept book, holiday, award, dinosaur, insect, DIY, transportation, tall book, pop-up, story book, board book, reference, magazine, series, new book, video, and audio and were easily expanded by combining age tables or fiction genre. Also, new simplifying methods of building call numbers with collection codes were suggested.