I would highly recommend any of the books in this series by Cheri Meiners. Join In and Play is a great book for parents whose children are shy or may avoid social interactions. It offers a variety of ways they can be included and have fun with their classmates and friends, even illustrating how to ask to join a game or play quietly beside another child. It also would be helpful in helping a more confident, popular child to reach out to quieter, less engaged peers.
These books caught my eye because the writing level is just right for pre-K and kindergarten children. Truthful without being preachy or overly wordy, the series shows children and family members from many different ethnic groups in the colorful illustrations, and each book addresses issues which are developmentally critical to this particular age group: sharing, taking turns, being afraid, listening, respecting others, helping out at home, etc. These books have given us a starting point to discuss problems at school or interacting with others, and have helped my son to have more empathy for his peers....I am hopeful that this quality will serve him well as he continues on to kindergarten and elementary school. It is exciting to hear him use ideas from this series to problem solve.