Ok I'm a dad. If you have kids, you have to try spectrek with them.
It uses GPS, google maps and your video camera.
It uses GPS to place a number of ghosts in your neighborhood. When u hold the phone flat it shows a map with the location of ghosts, when u hold it upright it automatically becomes a camera that shows what is in front of U plus a superimposed image of the ghost. As you approach the ghost it becomes larger, once you're next to it, u press a button and it cages the ghost.
My 6 y/o daughter had a blast "hunting ghosts". It was also a very nice walk around the neighborhood.

Hey mesh..there's a 3D version of that fall down game. I was playing it lastnight when you recommended your fall down game. It's not that bad.