Childhood activities are moving indoors because if you leave your kid out in your own yard, someone will pick them up, rape them, and dump them in a plastic bin in an abandoned landfill. An adult can't spend all day sitting around the park or yard with an eye on the kids, the adults have to be in doing adult things much of the time(laundry, cleaning, cooking, etc).
When we were kids, the park was a safe place. An 8 year old could walk down the street and spend ALL DAY there without fear of anything worse that a fight with another 8 year old or maybe falling off the jungle gym. Not anymore. Too many predators, both adult and older kids. I started to see the beginnings of this when my (7 years younger) brother was a kid. I spend all day at that park and never had an abnormal problem. I got into a few fights, played basketball all day, normal kid stuff. By the time my brother was of that age, the park was controlled by a group of kids from a new housing project up the street. White kids were no longer allowed, anyone white who showed up was told to leave, if they refused they were beaten up. If they came back they were beaten up worse. The park was full of thugs by day and drugs by night. Now it's just an abandoned lot because the town had to remove the equipment and basketball court to get the people to move on.
Now, that's just that one park... but it's not, really, it's many parks. Without the parks, where do your kids go? Boy scouts... our town Scout Leader, who had served a 'clean' 40 years and was practically a town saint, was just sentenced a year for sexual assault on a child, and many more are coming out now. Church? You've got to be kidding. Maybe the library, but that's no place for a kid to spend extended time.
When you combine these things with what is described in this thread, the stupidly litigious and overprotective to a point of hindrance philosophy we see now... where the hell do your kids grow up?