This yahoo story, Have Playgrounds Become Too Safe For Kids? highlights these issues. Kids are not challenged and enriched with playgrounds. They don't develop their motor skills, nor do they overcome their fear of heights, or figure out how to shake off a scraped knee. Worse, schools are banning games like tag, red rover, dodgeball, and running in a few schools! This is a horrible omen for the next generation of adults. Not only will the obesity rate continue to climb for the next generation, but using exercise for fat loss will be much harder. These kids will not even have the physical ability to perform low-intensity physical activity, let alone more-effective high-intensity exercise.
Physical play, like roughhousing is also very important for social, cognitive, and intellectual development. Physical play has a strong social component, with winners and losers, just like the real world. Additionally, kids learn that it takes effort and there are some bumps and bruises along the way.
The dangers of a non-physical world are dramatic and long-lasting. While much has changed in our environment since 1977, not much has changed in our DNA over the last thousand years. We need to move and be physical; it is an integral part of our biology.