Internet,Ipods,Play Station, just to mention a few.
True. Also, I think subdivision layouts and the "subdivision mindset" have something to do with kids not running around in herds, like we used to.
Also, I suspect there really is more danger for kids than there used to be, in the form of sexual predators.
But I think there's also a rather powerful "ninny state," which does things like replace playground equipment with "safe" stuff, plus a somewhat suffocating overprotectiveness on the part of parents.
Not to mention a 24 hour news industry terrifying parents with stories of child abduction, child rape and child murder. Many parents are terrified to let their children out of their sight.
There was a story in my home town about a local boy who'd been reported missing. The reporter on TV mentioned that the boy had been out, unsupervised for 8 hours and acted as if the parent should be charged with child neglect.
When I was that boy's age I'd be out from just after breakfast until dinner time and my parents only had a vague idea of where I actually was. I may have been playing ball, I may have been swimming at the lake, I may have been in my tree fort or building a new tree fort or fishing in the creek. It's a different world for kid's these days.