S.P.
I just started my 5-year-old on PeeryPiano.com and both he and I LOVE IT! You receive your lessons via video and once your child is ready you video his playing, post it on the site and the teacher (who is an international award-winner) personally responds with her own video response. I had concerns that it wouldn't be as good as in-person lessons but I actually prefer it because we can watch the lesson videos whenever we want. I actually taught piano for over 10 years and I prefer this to regular lessons.
Sorry to go on, but one more thing I love is that there's no driving to lessons and it costs a fraction of what regular lessons cost at $20 a month.