[spanhandler]

If you want support from an app for piano and especially if you already have a keyboard or digital piano with MIDI out, I would strongly recommend Simply Piano on the iPad. I'm not affiliated, just a very, very happy user with a young kid getting more out of that app than I would have imagined—I started off keeping pace, having played a few instruments but not piano before, but when your kid spends every spare minute on the damn thing it's hard to keep up, after they get the hang of it.

It's not so hot at form—it tries to teach and reinforce it but of course it can't dynamically check that you aren't screwing up—but is great at most other things. Heavy focus on playing recognizable and fun music (they license tons of stuff) to keep up interest, with arrangements adjusted down as necessary. Long, segmented "curriculum" plan with some branches, free play modes on songs you've "unlocked", sheet music available and play modes that scroll the page for you. It's really nice.