Some Nanite Project headcanon doodles and their explanations, going from left to right:
I doubt that Rex would say this exact thing but the idea is that, being a fairly lonely kid and someone who was probably easily bored even back then, Rex would’ve pestered the people around him a lot, which you know. Fair. I hc him as being a lot like he is now, but obviously more childish. Because literal child. So very inquisitive, curious, trusting, and empathetic, but easily bored and reckless. I feel like he would play on his own (or accidentally injure himself climbing on industrial equipment which just seems like something he just. Did. It also makes him currently being an adrenaline junkie make more sense) until he got bored (or injured) and then pester all the scientists around him that would tolerate him for long periods of time.
Next up is that Van Kleiss and Violeta Salazar (Rex’s mom) had similar or complimentary roles on the Nanite Project and thus worked together a lot. Judging by how Van Kleiss talks about Violeta in Written in Sand, they probably had a similar dynamic to Rex and Van Kleiss in that episode, except with a lot less sand and threat of imminent demise. This would be really funny to me. Also pictured Rex just hanging out, because he seems like he would be a momma’s boy. He is acting out a very tense and dramatic romance between these two cars and they are finally about to kiss. I also feel like current Rex would love K-dramas.
I honestly don’t think Van Kleiss hated or disliked Rex when Rex was a young child. I feel like he would’ve found him amusing at best, annoying at worst, and sort of weirdly endearing, but never being outright mean to him. Based on the tolerance he has for Rex’s shenanigans in the show while he has almost none for anyone else, even his own allies, this had to have started somewhere. If Rex was a chronic botherer, then someone who doesn’t get easily or outwardly annoyed would be the perfect target. Van Kleiss also still is not explaining shit, his favourite activity.
Finally, Rex naming ZagRS. This is actually one that I’ve had since I was about 14-15 because there’s no reason given for her name to be what it is. Like it’s not an acronym like GLaDOS (Genetic Lifeform and Disc Operating System), and it sounds kind of like Zagreus, an ancient Greek deity that I cannot find anything on except for who his parents might be and that he might have some connection to Dionysus. In canon, Caesar mentions that Rex speaking Spanish makes him laugh because he has trouble with pronunciation. This recently led to a whole-ass rabbit hole where I came up with the theory that Rex has just always had trouble pronouncing words because of ADHD, which fed into my already existing headcanon of Rex having named ZagRS. Also I think that Caesar was another person Rex bothered a lot because Caesar has a tendency to be pretty chill. I kind of wonder if they had to keep Rex away from ZagRS because she was designed to destroy any nanites that got out of the holding tanks.
I honestly love making these theories and headcanons so if you want to see more or have questions just pop me an ask.