Sometimes I think about how the Tarsus IV hellscape is, chronologically, where TOS Kirk's history begins.
Virtually every popular idea about who he was before that, or what the details of his life and history were prior to Tarsus IV, come from outside the show—either decades-later retcons nowhere suggested in TOS, or just pure fanon. In the show, it's a long time before we even hear that he was born on Earth. He volunteers less information about his family and pre-Starfleet life than Spock.
Pretty much the only thing we're told about his life experiences that could possibly indicate something about him between his birth and the famine on Tarsus IV comes from "The Paradise Syndrome," in which as a stranded amnesiac, he has a strong but uncertain impression that he'd never felt happiness or peace in his life before. That is it. So the whole idyllic rural Midwestern childhood with wonderful supportive parents deal is something entirely external to the show (and, tbh, I think very much part of a later push towards making Star Trek in concept and Kirk in particular more "comfy" and accessibly heroic for blockbuster purposes).
But Kirk's earliest appearance in the internal timeline of TOS is as the thirteen-year-old survivor and eyewitness to Kodos's crimes, one among nine boys and men to survive, and in no way distinguished from the other eight at the time. There's basically nothing to him before that collective experience; the coup/famine/genocide there are the first of the many atrocities and horrors that define so much about his life, but they're also the first anything about his life.
In a way, it tracks that "The Conscience of the King" contains the storyline that, had the writer been allowed, would have mentioned a parent of Kirk's (his father would have been a scientist murdered by Kodos, and Tom Leighton the RA to Dr. Kirk who was scarred in that event, hence Leighton's highly personal appeal about "the bloody thing he did" to Kirk as the episode opens). As far as TOS is concerned, Jim Kirk's life as a character begins with Tarsus IV.
