Every app wants to be a rock star, Numerosity by ThoughtBox comes up close. It is amazing how an educational math app that is simple is also very entertaining. Basically the app (like many reviewed here) consist of answering math equations. The difference in this app is the pacing.
The pacing is fast. The app encourages you to answer the questions as fast as you can (with both visual cues and audio cues). The math for me (a grown man) is not very challenging, but I found myself playing the game level after level.
The graphics are simple but above average. The sound effects are great. Although I loved the music, I can see how it would become irritating after a while. The app does have an in-app store to buy more chapters, but you can buy them all for $5.99. It has enough content in the free version to make sure that your kids will like it. Overall a great addictive math game.
I played it on my full size iPad (provided by the publisher). It is only available on the Apple App Store.