Little Piano is a free, educational piano app for kids (and their parents).
It will turn your iOS device into a piano with 13 keys, 1 octave, and good-quality sounds. There are various instruments, not only a piano. Whether you're just starting to learn piano or if you’ve been playing for years, Little Piano is a great app.
To learn new songs, try the Follow Me Guide within the app that shows you how to play simple melodies like Happy Birthday, Twinkle Twinkle Little Star, Old McDonald, and many more. The ad-free version, Little Piano+, is also available for 0.99$.
Hope both you and your children will enjoy Little Piano.