Piano Books

my kids are also using Piano Adventures - they're 7YO and started with the "Primer" level books, but there are also the "My First Piano Adventure" books for younger students:
http://faberpiano.com/myfirst/

Hi J.! I am a piano teacher and I love the Piano Adventure series by Faber and Faber. The Alfred Piano Series is also wonderful.
I do want to advise you to take it slow with your son, unless he is a proficient reader. Keep his practice time very short and don't push. Most kids who start at a very early age don't progress as fast. I was 7 when I started piano and very quicky surpassed my friend who had started at age 3. That is the case with many kids. I don't take students until first or second grade. When I am approached by parents who want their 3 or 4 year old to take lessons I direct them to a Kindermusik class. It gives a great musical foundation to preschoolers!

Good luck! Music is a wonderful gift to give your kids!

My daughter uses Piano Adventures.

I'm a piano teacher as well, and I second the Piano Adventure series and also suggest the Music for Little Mozart books, you can even buy them in a pack with flash cards, a mouse and a bear stuffed animal that can be used to help your son. I use this for my younger students most of the time and they love it.

Good luck! :) Music is such a wonderful gift to give a child!

Music for Little Mozarts - Suzuki - Dozen a Day