I read this review of Anna on AMC+ this morning. The plot of adults all dying and kids building their own society is the plot of a Star Trek TOS episode called Miri, as pointed out by the review.
Overall it’s a negative review. But it has enough intriguing aspects to it that I wish I could see it. I don’t think there’s anything else I want to see on AMC+ though, so it will have to wait.
It took a bit of googling as I swear I saw a riff on the concept outside of Star Trek, and it looks like I’m thinking of a specific town/questline in Fallout 3.
I remember that. People were pissed off that you couldn’t kill children in Fallout 3, they disabled combat in that town. But the main difference there is that when you grew up enough, the rest of the kids threw you out of the town and you weren’t allowed to return.
Cixin Liu of Three-Body Problem has a novel with a similar premise, Supernova Era. A distant Supernova washes the Earth with radiation that will kill off everyone over 13. So it’s a desperate race to teach children how to keep the world going before they die.