Pre series really interests me because I want to know why Sam is the way he is with Dean. Watching the ep with Sonny and Sam saying John told him Dean was on a case or whatever instead of abandoned and hearing Sam didn’t know Dean carried him out of the fire makes me so curious about how many other completely different experiences the brothers have growing up. What other lies did John tell Sam that affected Sam’s view of Dean? What lies did John make Dean tell and what secrets did Dean have to keep for Sam’s well-being? Dean’s experience of their childhood was practically raising a kid while being a kid, but Sam didn’t think Dean would know anything about children. As much as they were raised inside each other’s pockets, their lives were completely different and I don’t think Sam has ever considered that, but the fandom should.
Of course the real problem behind the lack of interesting pre series fic is that people think Sam’s behavior is fine. No one is exploring Sam’s flaws, because no one sees Sam’s flaws. So boring.
I also find this really interesting. We only get the smallest glimpses of their lives pre-series, but there’s just an important revelation about Dean’s experience versus Sam’s in most every one. Overall, Sam’s perceptions of their childhood have been rather warped. Like what you mention with kids, there was also Sam’s seeming surprise that Dean could cook, despite the fact that Dean often did (and still does) cook for Sam. And Sam supposedly always “looked up to” and wanted to be just like Dean his whole life…only not in any of the flashbacks we get is that shown. It really does make you wonder.
And there’s almost a sinister sense of mystery around what Sam doesn’t know. I mean he didn’t even know Dean was scared of flying, say nothing about whatever was behind Dean’s shifty response to Sam’s praising their dad for not beating them in Nightmare or whatever Dean couldn’t manage to say aloud in DSOTM.