I noticed that there were several comments in other threads about explaining Buddhist principles to kids. I am a childrens librarian and here are a few of my favorites:
Zen Shorts and Stone Soup both by Jon Muth
Basho and the River Stones by Tim Myers
Selma by Jutta Bauer
Samsara Dog by Helen Manos
I'd love to hear about other Buddhist themed childrens books that you've liked.