Today things are different. Parents worry more: Your kids might get kidnapped/raped, might do something bad and 'get in trouble', or take drugs, or get a sunburn, or not make it into the college of (your) choice. The horror. The horror. The horror. So summer is filled with classes, sports, music lessons, and family cruises. As many as possible conducted indoors.
Related to this, I think, is a change in the distinction between "indoor" behavior and "outdoor" behavior. In my childhood, using a 4-letter word or burping in front of others was the height of ill-breeding, and could only be enjoyed beyond the earshot of adults. When outside and running the neighborhood, each child could vanish into the special world of childhood for some or all of the day.
To hear my father (born in 1920) tell it, in his generation the gradient between indoors and outdoors was even steeper. For boys, at least, you were either sitting in auntie's parlor in a starched white shirt, or you were outside smoking cigarettes, starting fires, stealing stuff, and getting into fist fights.
Today, burping and bad language are ok everywhere, but fist-fighting and cigarettes are ok nowhere. Are things better now, or worse? As a parent, I prefer today's approach. But that's probably just because I've fallen prey to the parental paranoias.
I sometimes worry that today's kids lack the free time needed to discover oneself. Or ... are we living in a world today for which "discovering oneself" has become as outmoded a concept as starched shirts in auntie's parlor?