What about the Babar books? Those are pretty simple, and it's definitely at a lower vocabulary than The Little Prince. I think Babar was the first book in French I ever read in school. Also, something that's worked really well for me is reading children's books you've read in your native language in French. Like the Madeleine books and Dr. Seuss. It's good for learning basic vocabulary as well as some simple idioms and grammatical rules. Some books are even available in half-French, half-English so you can compare as you go along! Good luck, and don't worry -- it always get easier.