Fashioned from a gourd, a hardwood plank and some scraps of metal, this elegant little instrument is called mbira in central, western and eastern Africa, where it originated. It was a Christmas gift from my parents many years ago, I've played it with my kids on my lap when they were just a few months old, then a year, and more, until their thumbs were long enough to reach the keys. Intimate, resonant and beautifully tactile, it invites play and defies mastery because of the counter-intuitive left/right shattering of your expectations of how the scale should run. But you can make chords with a single thumb, and a little chorus with both. For a kludgy, digitized sense of what it sounds like, try this Flash-based thumb piano. For the real thing, go to any good music store and ask.