We're not here to make decisions about your world for you. What makes you think that this question doesn't have many equally valid answers?

@sphennings It does not because there are clear criteria for what the kind of apocalypse should achieve. A nuclear apocalypse would leave massive radioactive fallout for generations. An asteroid could cause a long lasting climate change. Zombies/killbots would not just disappear over night without a strong central paramilitary organization rising in the aftermath, etc.

@sphennings Yes, I am having trouble thinking of a single good fit, most post-apocalypse tropes are bad fits for 1 or more reasons (I've expanded my answer to explain this better.) If there are more than 1 good fit, the balance of being traumatic for the survivors and leaving the world unscathed for the next generation should make one answer fit better than others.

Remember that while answers can be better or worse than others while still being equally valid. It seems like what you're really wanting is a justification that an apocalypse will not have multigenerational psychological impacts. What makes you think that there's only one justification for one apocalypse that will suffice? Seems to me like you could make an argument for the strength and resilience of the human spirit leading to this for most apocalypses where humanity isn't completely wiped out.

@sphennings even if you were to make a compelling argument to that effect, it does not change the fact that one apocalypse is more likely to produce the desired outcome than another. The most ideal apocalypse will still create the easiest suspension of disbelief. Questions with more than one possible outcome are allowed as long as there are criteria for a best possible outcome.

It's not an exact match for your synopsis by any means, but The Stand by Stephen King does a very good job of setting up more-or-less what you want (at the start of the book, at least; you probably won't want the weird stuff). It's a very plausible pandemic scenario with an unfortunately believable narrative.

Concerning your contention that "I can't just say some god snapped his fingers and a bunch of people turned to dust because that would honestly not be that traumatizing for the survivors": I would highly, highly recommend that you want the series The Leftovers, which deals with the psychological aftermath of a world like this.

"... They have had peaceful and generally unremarkable lives ..." I am having difficulties conceiving of an apocalypse scenario that leads to the youth psyche that you describe. Yes, post-apocalypse born or raised children might have different perspectives when it comes to what we consider luxuries today eg. "I gutted this Ferrari because it has seats that look neat and I wanted them in my treehouse" but their attitudes might be totally flipped when it comes to what pre-apocalypse people considered consumables eg. "I only take out the toilet paper on special occasion, 5 sheets max!"

Also, "the pressures of modern society"? Please. Modern society is a downright 24/7 spa experience compared to the abject suffering that people toiled under during ages long past without the modern infrastructure and "guts" that keep our systems going. I would much rather like to be subjected to the "modern" pressure of, for example, being expected to get a university degree or a well paying job compared to being subjected to pressures like "If I don't grow/scavenge/hunt enough food, my family, friends, and everyone I care about and love might die in horrible agony as they starve"

I'm having trouble with the premise that traumatized adults wouldn't inflict trauma on their children. Adults often transfer some of the symptoms of their own traumas to their children. ( talkspace.com/blog/generational-trauma ) By some definitions, PTSD is contagious: scientificamerican.com/article/… Theories of contagion also work for crime ( ojp.gov/ncjrs/virtual-library/abstracts/… )

Thanos. "Today it's a paradise"

You are romanticizing those scattered villages. Thomas Hobbes did live. Those people's lives would be solitary, poor, nasty, brutish, and short. And plagued by roving bands of marauders.

This may seem like a trivial quibble, but could you please give us a comprehensive definition of a "well adjusted" children? Normally such things would entail being adapted to a specific environment and social (if the environment is social). That happens in war-zones today, they're adapted to their environment, but wouldn't fit in in more peaceful circumstances. What about the inevitable oddballs who get flung-up in any society? Must there be none of those? What about gangs, subcultures/countercultures etc.? Groups of different ages? Please define what counts as well adjusted.

Cont.. I can't help but think of Camino from the Star Wars franchise. The clones, all identical, all conditioned into their roles - they don't have any of the issues of non-well-adjusted members (except the 99ers).

Do you have to say? Can your story just walk around it? Post apocalypse is so over done now that I wonder how many readers would mind if you just left most of it as a blank given.

The kids don't know what happened, the parents won't talk about it and hence you don't have to.

@fredsbend Yes it is important to know what happened. I would like remnants of the event for characters to interact with: just not the kind of remnants that make survival harder. Like maybe the kids like to play on "flower hill" which is actually a mass gravesite where the flowers grow especially well, or maybe they like to play in the old trenches and bunkers. What kind of features these are will be impacted by the event, but yes: most grownups will probably be reluctant to talk about it.

@Dragongeek This may apply to you if you are lucky enough to fit into one of the privileged slots in modern society. There are a lot more people than privileged slots. The homeless bum at the train station might well wish he was a farmer, at least he'd have a purpose then.

@user253751 This is nonsensical and completely ignores the reality of homelessness--which is not a function of "modern society". If you were a "homeless bum" today, what you'd be in the past is a probably dead homeless bum. Like, just a couple hundred years ago, it was the law in England that vagrants should simply be put to death. Just because there are people unemployed, does not mean there are no jobs available just like plenty of people still die of starvation despite the fact that we produce an enormous global food surplus. Also, farming is not easy. It's hard, rarely rewarding labor.

@Dragongeek In the past, you didn't have to impress a CEO with a Harvard MBA to not be homeless.