...these are books for children, with Bag One one having the earliest readers and then progressing up the ladder in reading ability. Each bag is numbered, but many kids don't bother to read them in order. In order to keep track, there are cards that kids can stamp when they have read each bag. The 100th bag is a different color and kept in the Youth Services Librarian's office. People have to ask for that bag and then receive a prize.