It wasn't uncommon for kids under 18 to be out that late just a couple of decades ago.

In the 90s/early 00's 10pm was like a weekday, school night curfew.

My parents generation was so laisse faire with their child rearing that they ran ads to remind them to go figure out where we were.

As already said it was a PSA ran on TV in the US up until at least the 90s I think. It's not really a different animal when you think about it; at the height of summer the sun doesn't set until around 9 (at least in the northern half of the US), so the PSA is running probably half an hour to an hour after its gotten dark. Which was a pretty typical time for kids to be told to be home. Ie "be home when the street lights turn on." So the ads basically saying "your kid was supposed to be home over 30 minutes ago, are they back yet?

Edit: adjusted the times because I actually bothered to check when sunset is.