Where do the children play?

I think that something else changed and should be added to the analysis: the number of children. There are less of them so there are less chances to reach a critical mass that lets kids play together every day. When I was little it was common to have between 10 to 30 of us within the fence of our city building. Parents and grandparents were looking at us from the windows but they were probably hearing us scream and play, a sign that all was good, and we were left alone to do what we liked to do. Where do you find 10 kids together now, if not at a school or in another organized context (organized by adults) ?