I have a memory of a 'play for the day' sometime in the 1980s, of a post-Apocalyptic community/tribe who live in a green valley, somewhere in England, but they had some very strict rules that the children didn't really understand, like eating animals. But it turned out that the adults, who remembered the times before the nuclear war (I assume) couldn't help it, because they craved such food, so they ate meat they caught secretly. But this slowly killed them all (because of radiation???) and it left the kids by themselves as all the adults succumbed.
I am sure it was something like that and could potentially dovetail with the OP ending. But...
...it doesn't quite make sense, as surely everything, including plants would be radioactive - unless they were spinning a 'silent spring' sort of vibe that some animals concentrated the poisons. But all the radioactivity would be building up in the humans as well.
It's not threads, I've had a look at the plot summary and the final scene on Youtube.