Here is another app to add to the list to encourage physical activity in children - Big Cat Race (and its free!). Basically you pick an avatar - lion, leopard or cheetah. You pick a level - easy, medium or hard. Then you pick a race - either number of steps, timed or free run. Then get ready to race. When the iphone says go the child runs holding the phone (the iphone screen goes black while the race is on so be sure to tell the child there is nothing to watch while they run). Then when the race is over you get to see how long it took, how many steps you took and what your speed was. It saves your times based on the profiles you create. You can even play back the race and watch the animals.
This was a fun app that got a 7 and 8 year old running all over outdoors to see if they could beat the big cats. We found that if you really want to win the race try the 10 step race. They seemed to win that race consistently. Occasionally they did get frustrated because they ran as hard as they could on the two minute race but did not even come close to winning when they watched it playback.