My mom was a sahm, so she was mostly home. My summers were like rolyco describes above. It was a different time (I'm old ;)), and kids had a lot more freedom than they do now.
I don't know too many kids who are latchkey in the summer, but sure, that could be a reason for vegging out in front of the tv all summer. But I would hope these aren't little kids you're talking about. In many states, it's illegal to leave kids home alone under a certain age, and I wouldn't think it would be safe.
In my city, there are lots of inexpensive things to do in the summer. There's even a very cheap summer in the parks program that is aimed at keeping younger kids busy while their parents are at work.
I would hope not, either, for the reasons you stated.
downtime isn’t what it used to be. dh is home with the kids all summer, and the past decade-plus has taught him to go ahead and schedule activities and camps in the mornings. vampire families are everywhere. some of them allow their children to stay up (and apparently use the phone) until all hours of the night and to sleep away the summertime prime-time cool morning hours, and others haven’t necessarily allowed their children to reverse cycle their sleep but are managed by a parent who can’t be “rushed” into getting his or her own or even his or her children’s poo together before noon. the fact that the (around here overwhelming) majority of children—even those with a sahp—go to at least some activities or camps (the quality and number of options here is very high) thins the neighborhood hoards even further, especially through the early afternoon. factor in the number of parents who consider it neglectful to allow groups of children (even pre-teens) to roam outside of direct parental supervision, and unless your child is a hermit or you are a big fan of trading helicopter-supervision playdates (which usually translates into your kids playing video games at a neighbor’s house, or the neighbor kid(s) at your house complaining about the fact that you don’t have any video games and whining that they want their wiiiiiiiiiiiiiiiiiiis), and “lazy” and “unscheduled” summer weekdays often mean stuck with no one but your parent and sibling(s) for company. while my kids can have something like the roaming-the-neighborhoods-in-gangs environment dh and i remember from childhood on weekday evenings and weekends, it simply isn’t reliably or often available on summer weekdays.