The Washington Post has a recent article about parents, governments, and activists being concerned that kids don’t get enough time outdoors anymore. The Daily Mail has a somewhat similar article, addressing the psychological issues of nature deprivation, and the narrow range of space that children tend to roam outdoors.
These articles sound like they are about the same thing, but they read quite differently. The Washington Post article cites some research about kids’ diminished outdoor play time, and offers a lot of anecdotal evidence implicating modern media, especially video games:
[Last Child in the Woods author Richard Louv’s] views have touched a nerve—in an era when people tell stories of backyard play sets that are barely used and children who are so accustomed to playing video games that they use their thumbs to ring doorbells or dial phones.
The Daily Mail article also cites research about kids’ diminished outdoor time and its effects. That research, however, implicates parents, not media, for too much hand-holding and too little freedom:
[Speaking of her son, one mother] said: “He can go out in the crescent but he doesn’t tend to go out because the other children don’t. We put a bike in the car and go off to the country where we can all cycle together.
“It’s not just about time. Traffic is an important consideration, as is the fear of abduction, but I’m not sure whether that’s real or perceived.”
I don’t have any conclusions to offer; just wanted to offer something to think about.
Geek Studies 
Analysis: Rearing children in captivity (http://news.bbc.co.uk/1/hi/education/6720661.stm)
I remember playing in the sand dunes a mile away and sometimes walking/biking to piano lessons several miles away. I don’t remember my parents setting limits on where I could go. I think it was good for me.
I think it was good for me, too. We kind of saw both sides of it in my household, though. I had pretty much free reign of overgrown railroads, wooded areas, and the entire Boston transit system as a kid. My brothers, on the other hand, had a more restricted range to wander, and had to carry pagers (later, cell phones) so my parents could keep better track of them. Years later, my parents acknowledged that they let me get away with more because I did well in school, and therefore must have been responsible. (Being a geek pays, kids!)