Tenuto/MSO Apps

The Tenuto app is in the app store for around $3.99 I believe. Its definitely money well spent for youngsters. It takes you through basic music theory in a fun interactive way. Key signatures, note names and intervals are just some things covered. So far the kids in my lessons love it so much I've limited it to the end of lesson times or they get addicted. It also has sound so you can do some ear training. Its great for guitarists and pianists also, as has Fretboard and keyboard note identification.
The MSO (Melbourne Symphony Orchestra) also has an app called MSO learn. It encourages kids to learn about different sections of the orchestra and has interviews and demonstrations. This is also free so that's a bonus!

Happy practicing!