Are The Little Traitor Dudes For Children's Defense, the "negative" counterparts of The Delightful Children From Down The Lane really good guys or just bad guys who were brainwashed like what happened with their counterparts?
Given what we know now of Sector Z and the true nature of the Delightful Children from Down the Lane, was Lenny's attempt of a reverse mole ploy a sincere attempt to break free of the brainwashing before the delightfulization returned? This fanfic goes with this idea.
To what extent are the Delightful Children's Hive Mind and monotonous personalities? Does their delightfulization dilute their individual personalities, or do they as "good children" intentionally speak and act as a unit while showing little personality? In U.N.D.E.R.C.O.V.E.R. we see that Lenny can leave the group and act independently, and while he keeps his eerily blue eyes, he never once speaks in Creepy Monotone and acts pretty normally (though this may have been faked in order to divert suspicion). In the same episode the other Delightful Children are able to speak with him separately, which neither the KND or Cuppa Joe seem to find peculiar. They also have a habit of muttering separately when Father intimidates them, or individually grumbling when they're irritated, further demonstrating that their unison speaking might be intentional. Further evidence is that one of the the Annoyingly Cute Triplets in C.A.K.E.D.F.I.V.E. is implied to be Grandfather's mother, despite them similarly acting as one delightfulized unit and appearing to be linked together. Notably their Rowdy Hooligans and Interesting Twins counterparts are also able to act individually, despite also being presumably delightfulized.
Is the global organization a rebellious group of kids devoted to defying adult authority? Or a benevolent, somewhat Knight Templar-ish group protecting the children of the world from those that wish to harm or unjustly oppress them? Although OP: Z.E.R.O. seems to confirm on the latter, some viewers tend to scale strictly on the former.
Or are they straight-up Villain Protagonists with a Sympathetic P.O.V.? Considering their rebellious and violent behaviours, this was a lot more plausible early on in the show.
Does the KND inadvertently continue a Cycle of Hatred by decommissioning operatives who turn 13? The older members of the KND would likely have no reason to arbitrarily turn on their friends and join up with the teens and adults who have been menacing them for most of their lives. But the KND rejecting them and trying to remove their memories could result in former operatives feeling betrayed so they devote themselves to destroying the organization and all it stands for. Those who are successfully decommissioned no longer have any type of loyalty or camaraderie for the KND and easily recruited by their former enemies because they don't know any better. "Operation: M.A.U.R.I.C.E." and Numbuh 12's betrayal seemingly supports this theory.
Building on this theory is Cree's behavior. While it's made painfully clear what side she's on, there are some hints that it might actually be because she crossed the Despair Event Horizon over growing older rather then just being a traitor. In "Operation: M.A.U.R.I.C.E.", when Abby bemoans the fact there's nothing she can do to escape growing up, Cree gets excited because she's been waiting for Abby to say that, hinting that she went through something similar and didn't have anyone to pull her out of it. Additionally, there are several hints throughout the series that Cree does genuinely want to make up with Abby, her own terms or not, but mishaps continue to happen that cause her to double down on her ideals. Viewing her like this turns her from an unrepentant traitor Card-Carrying Villain to a Stepford SmilerTragic Villain who ruined every positive relationship she had outside of her parents simply because she viewed it as the way things are supposed to go.
The entire show is a game a bunch of kids are playing, or a story they made up. (This theory seems to be gaining ground on 4chan)
And adding on to that theory, Numbuh One is a kid who possibly moved away or died. Likely the former, because Numbuh One eventually returns.
Knowing what we know now about Lizzie Devine/Numbuh Vine according to GKND, did she REALLY love Nigel or was this all just a ruse? Or was it a ruse, but she actually fell for him at some point? On the same topic, it could be possible that every example of Lizzie being an idiot or oblivious to being in danger (like in Operation D.A.T.E.) shows she's been engaging in Obfuscating Stupidity the whole time. And also, was she being purposefully annoying towards him in the later half of the series as an attempt to make him break up with her, but since that didn’t work, she ultimately had to end it between them in Operation G.I.R.L.F.R.I.E.N.D?
Rachel's reaction following Nigel and Lizzie's breakup. Was she merely feeling guilty for contributing to it or was it heartbreak caused by an apparent rejection towards her from Nigel's part?
Jerry from BULLIES. While on the surface his story about wanting revenge on Numbuh 4 is sympathetic, we never really got Numbuh 4's side of the story either, just that "he deserved it". Was Jerry being entirely honest and Numbuh 4 just thought he deserved his permanent wedgie for being a nerd, or did Jerry do something to Numbuh 4 first and he refused to own up to it?
Was Mega Mom being Innocently Insensitive by throwing her son a 13th birthday party, or was she hoping that by exposing his age to his teammates he would be pushed into villainy?
Despite Mr. Fibb admitting that he was driven to villainy because Lasso Lass didn't go to the prom with him, he was quite freaked out when she expressed interest towards him as adults. Was he uncomfortable by her sudden interest and aggressive way of showing it, squicked out due to how much she's aged, was he simply just that awkward around women, or was it because he was gay and had since come out (while still being bitter about the prom incident)?
Why did Stickybeard save Sector V from the Great White Asparagus? Was it because he didn't want a vegetable to get one over on him, or did he think such a fate would be too cruel even for his enemies? His dialogue could be read either way, and it's possible it was a mixture of both.
fanfic goes with this idea.