I recently discovered a new app for young learners from the makers of Khan Academy called "Khan Kids." I haven't spent much time on it personally, but I am a big fan of Khan Academy so I recommend that you try it with your kids. Please let me know what they think about it in the comments.

khan1

Google Play Android Version - Here
Amazon Kindle Version - Here
Apple Version - Here

Khan Academy, sponsored by Google and the Bill and Melinda Gates Foundation, is a non-profit that provides free, world-class online education.