My toddler daughter loves books but she's still working on how to take care of them. Like most little ones will do at some point, the other night she dismantled her favorite book. Luckily I got to it before she really pulled it apart and managed to find the cardboard spine avoiding the need to make a new one.
It isn't rocket science and I'll be up front in saying that this project is probably more about using the right(purpose made) materials than any clever technique.
Step 1: The stuff
You can repair books with gaffer's tape, packing tape, white glue and denim, whatever but if you want your repair to look like a "book" you'll need book binding cloth and PVA glue.
You can order those online or find them at most any scrap-booking store.
The PVA glue is designed to bond paper like no other glue I have ever encountered and book binders cloth is designed to take a lot of abuse from handling and bending as well as having a paper backing that lends itself to working with PVA.
You'll also need a broken book to repair. I'll leave that up to you.