We purchased this book - Celebrate Diwali With Sweets, Lights and Fireworks, by Deborah Heligman - along with two others in preparation for a Diwali party with friends, as well as an introduction to Diwali at my daughter's school for her classmates.
This one is the most complete we have found in terms of pictures and content, about 30 pages in all. The kids at my daughter's school (4 and 5 year olds) liked looking at the pictures very much, but the text is aimed more at the 6-8 year old range.
All in all, a worthwhile purchase that my kids will grow into.