The BOB Books app is a great app for teaching beginning readers. The books come in sets and they are not free, but at $1.99 I think they are worth it. They start with simple three-letter CVC words and build up in difficulty from there. I have a special love of BOB Books since that is how I taught my own son to read. Now with the app, kids can match letters and words with their sounds, great hands-on phonetics practice. It also gives them a sense of beginning sentence structure. If you want to try it out a bit before you buy you can get the BOB Books Reading Magic Lite app.