Control a bouncing color changing ball using the accelerometers in your phone.
This application provides amusement for my 3 year old while we wait at restaurants. I would gather from that that any child from age 2 to 4 would be equally amused.
As the ball bounces against the walls, it leaves a tail behind which will eventually slowly disappear. When the ball hits a wall, it's acceleration is reversed and ever so slightly reduced (friction of course). It is possible to get the ball bouncing very fast. Holding your phone so that the ball rests in one corner will slow the ball down.
Slide left and right to change the ball to a square, spinning line, ball that gets larger and smaller, and other interesting shapes. Slide up and down to change the size of the ball. Press the menu button to save the image you have created. Press and hold to reset the screen and place the ball where you pressed.