Had a child villager show up in my survival world recently set to flirty. I think it'd be a nice to have this specific trait completely off for all child villagers for obvious reasons.

Yeah it's weird to say the least.
But on a side note, what do you mean when you say the child villager showed up in your survival world? Was he born from a family, or just a random spawn in a village?
I'm asking, because when i first spawn in, or find a random village, i never see toddlers or children. It's only teens.
I've never randomly encountered a child villager.

The kid just showed up where I lived and swung open the doors to my house and walked inside. Basically made my house there home so I just ended up just changing there personality by using the village editor book, I had to get it by changing my game mode though. But I've seen a ton of child villagers before and even had a toddler villager at one point on my last world. I think they're pretty common? If you start building and have multiple villagers they'll eventually couple up and have kids on there own without you needing to intervene.

Oh, i'm not talking about a village that i manage, where the villagers eventually get married and have children on their own. I mean when i'm exploring the world, and come across a new village. I've never seen a toddler or even a child. Only teens.
That's why i was confused when you said a child villager showed up in your world.
But yeah, kids shouldn't really have the flirty trait. I don't how easy this would be to implement, but the unknown trait already exists in the game. Maybe traits for children, should remain unknown until children become adults. The flirty trait wouldn't be expressed or displayed by children in any way, and only be randomly attributed once they become adults. All other traits would be marked as unknown. For example, a greedy child, would have her trait marked as unknown, but in Chat AI, they would still talk and behave as being greedy. She would still be greedy, but it would be unknown. Only in adulthood, would the trait go from unknown to greedy.
Just a silly idea tho. Idk if this can even be implemented.