Those little cheap keyboards...

...they sell at Radio Shacks and what have you are pretty cool for kids. They have a number of built in songs that, when you play them, show the notes on the keyboard to play if you want to play them. My daughter has basically taught herself one fingered piano in a week - she only knew chopsticks and Mary Had a Little Lamb a week ago. Now she can play half the songs they keyboard has in it. I had to learn the organ out of a book when I was a kid!