When I was in first grade, my grandmother made me a book strap. I had never seen one before and she had to show me how to use it, but once she did, I was hooked.
I found this tutorial over at Design*Sponge and bookmarked it for a weekend project. Just for fun, make your kids a book strap and use it for library books. To start out with you'll need a leather or nylon strap. For detailed instructions and photos, head over to Design*Sponge.