I have a setting I'm trying to get started on where the vast majority of mankind has been killed off, and all that is left is a speckling of small villages pieced together from the wreckage of society.
The grown-ups in the setting were alive for the apocalypse. Most of them are pretty broken from PTSD, major depression, and/or crippling drug abuse thanks to the trauma caused by what was literally the most devastating event in human history... contrasting this older generation, the few children born since then have had things pretty easy. They have had peaceful and generally unremarkable lives. None of the pressures of modern society, but enough remanent tech to give them modernish luxuries (commercial grade farm equipment, refrigeration, air-conditioning, indoor lighting, etc.) which together have made them almost pathologically innocent and positive.
The thing is that there are many different kinds of Apocalypses, but all of what I can think of are poor fits for one reason or another: A nuclear/asteroid/global warming apocalypse would leave massive environmental damage that would last for many generations. Zombies, Killbots, etc. would not just disappear over night without a strong central paramilitary organization rising in the aftermath which is not consistent with small, scattered, peaceful villages. I can't just say some god snapped his fingers and a bunch of people turned to dust because that would not be traumatizing enough for the survivors.
I need something so horrible as to kill off nearly everyone and be able to break down the psyches of the collective adult population in the process, and then suddenly be so completely recovered that just 1 generation latter, everything is easy, peaceful, and positive for thier children. The central theme focuses on the diametric contrast between the traumatized and innocent mind; so, the best answer will not just meet these two goals, it will maximize this contrast.