highly recommended for atheist parents

http://atheism.about.com/od/atheistschildren/a/kids_index.htm

Also a book for the family:
The Usborne Encyclopedia of World Religions (http://www.amazon.com/Usborne-Encyclopedia-World-Religions-Internet-Linked/dp/0794510590/ref=sr_1_1?ie=UTF8&s=books&qid=1247082391&sr=8-1)