H.M.
My neighbors gave us a few John Thompson Beginning piano books. These are the same books my aunt used when she taught me 38 years ago and my 6yrold son is enjoying them. We also get things from the library occasionally.
For us, the key to happiness is keeping things light. Colin "warms up" and then we fool around together with the books, making up songs, practicing scales, finding notes, and/or reading music. We have a keyboard with lots of different voices which he LOVES. He practices 10-20 minutes a day (weekdays) and if he does (and homework is done) he'll get a bit of video game time later. At this point, I'm not aiming for skills, I'm hoping to get him comfy, have a routine of practice & have him like the piano so we can start a "real" teacher this summer. So far, so good.
He and his 9 yearold sis (guitar) love the video game reward system. Also, for every 10 minutes they practice, they earn time towards a "Colin" or "Audra" day - they get to plan the family's day, including menu. Fun stuff!