The University of Calgary's Canadian Exergaming Research Centre has been playing a lot of video games. Rather, they've been having a bunch of kids play a lot of video games. They haven't been playing Halo or Uncharted, they've been playing games like Wii Fit, Tony Hawk: RIDE, and Dance Dance Revolution.
After two years of researching third and fourth graders, they've found these games have a positive outcome on the kids. Third graders showed a 25% increase in balance while fourth graders showed a 29% increase. The study also comments on how these games aren't an alternative to using the gym or playing sports, but they can have a positive effect and can be a useful tool in fighting childhood obesity.
Kids, don't get too smug. This probably won't keep your parents from telling you to put down the controller and go outside.