d a-
This thread contains many recommendations for kid’s stories:
http://www.theyeshivaworld.com/coffeeroom/topic/please-share-recommendations-for-childrens-fiction
You can also use stories from T’nach; i.e. the story of Yerovom.
A trick that camp counselors (among others) use is to change details of secular fiction to make the story Jewish and appropriate. Encyclopedia Brown stories are good candidates for that.