Our 6 year old daughter is doing Number Bonds at Primary School, and we developed an app to help her (Above is a video of her brother playing an advanced prototype).
It seems to have helped her a lot, and now we've polished it up from it's humble beginnings into something we hope to be selling imminently
We've tested it on 6 year olds, and 9 year olds but we gave it to our 4 year old son and he got on surprisingly well with it.
The kids seem to really enjoy playing, but it was when we added the stars for how well you have done that their interest really picked up. They come rushing up the stairs when they've got 4 or 5 stars on the level they're working on.
By the time you read this post the game will probably be complete so check our products list if this is something you would be interested in.