An NYT reporter likes DragonBox:

http://www.nytimes.com/2013/11/14/t...-children-can-play-the-game-of-math.html
With Apps, Children Can Play the Game of Math
By KIT EATON
New York Times
November 13, 2013

[...]

The most impressive math education app I’ve seen has to be DragonBox Algebra 5+. What impresses me is that its clever design can teach all sorts of complex algebra concepts without making children feel as if they are learning mathematics.

The app is like a game, and it starts at an abstract level: The player has to match small cartoon icons with their matching “dark” alternatives, eventually arranging the pieces on the playing board so that only the magical “box” of the game’s title is left on the board. As the child plays through the levels, the abstract cartoon icons are eventually replaced with numbers and proper mathematical symbols, but with the same gameplay and sound effects.

It’s fun, and the graphics and sound effects are attractive enough to keep children playing. And while they’re playing, they are unknowingly learning some of the same math principles that you need when you’re doing algebra — addition, subtraction, balancing an equation, even concepts like parentheses. Play it yourself and you’ll see how much fun it is.

Perhaps the main drawback to this app is its complicated menus. If you’re going to use it with 5-year-olds, it’s probably best to keep them company so they don’t get frustrated by instructions they cannot read. It is also surprisingly expensive, at $6, but you get over 200 puzzles for your money. The app is on iOS and Android.