Here are a couple of Diwali Stories for Kids which you can find online.
1. From Learn English Kids a British Council site - an excellent Online Diwali Story for Kids . I love the interactive fireworks game at the end of the story. It will get anyone in the festive mood for sure!
2. Here is another Animated Diwali Story For Kids from the National Grid For Learning. It includes an interactive part where kids can rearrange the story.