This is "Provide Some Answers," which is a feature where long unresolved plot points are eventually resolved.
I have another column called "I Tell You What If," which is about comic book stories set in possible futures that eventually came true. Here, though, this is a little bit different because the future of the Legion of Super-Heroes (at least the part of the "future" that the Legion itself was set in) was treated not as a POSSIBLE future, but as THE future. So, for instance, if an issue of Legion of Super-Heroes said that Cleveland was hit by a meteor in 1981, then Cleveland was hit by a meteor in 1981.
One of these facts from the future turned out to play a real role in Superman's comic book series.
Adventure Comics #356's lead story was drawn by Curt Swan and George Klein and it was written by longtime Mort Weisinger Assistant Editor, E. Nelson Bridwell. In the issue, it establishes that in the future, rather than Mothers Day or Fathers Day, they just celebrate Parents Day, but for the Legion members who are orphans, they don't get to take part in the ceremonies...
I've always admired the way the Legion could be so casually cruel to each other. "Sorry, you guys are all orphans. So you're going to be on monitor duty, oh, and we're also going to give you bad food because that makes sense to us somehow. Suck it, losers!" No wonder the Legion are always so quick to believe that one of their own has turned on them when Legionnaires have to pretend to be villains. They're always such jerks to each other for no reason that when they seemingly give them GOOD reasons to think poorly of them, then it is easy to believe.
Anyhow, the five orphan Legionnaires head off on a mission and they are suddenly exposed to some sort of youth serum. They are taken to the Interstellar Orphanage where they are all put up for adoption.
Here's a problem. Brainiac-Five maintained his intelligence, so he knows what is going on, so he has to explain why Super Toddler appears to be from Krypton, a world that was destroyed over a thousand years earlier. So he explains, instead, that this kid is from Rokyn, the planet formed when the Bottled City of Kandor was settled there sometime in the past.
Eventually, they are all adopted by people from the same planet, but Brainy figures out that it was all a plot by the people of the planet to get some kids again because all of their youth had been killed by an environmental tragedy. In the end, Brainiac-Five returns everyone to their normal ages but also lets the people of the planet know that the problem with no kids being born on their planet is over now.