This colorful and easy-to-use app provides a way for children as young as toddler age to interact with music. PianoBall is available for iPad and iPhone ($0.99). Your child can choose from two different keyboards and a variety of songs and sounds.
Kids can either play their own tune or follow the "magic stars" to learn how to play one of the programmed songs. One great feature is that it has parental controls, so you can choose what skill you want your child to focus on!