I found out that 2 kids shoved each other and then fought but there's no action for this in the pie menu. There's hidden unused bad relationship animations exclusively for children vs children and teens, they practically could shove and attack teens or children. I remember the Goths kid would attack out of nowhere in vanilla based game with no expansions. Is there a mod to enable this? This was not consistent, and never happened again.

I think they still can, but only if they have a very low relationship score with each other, possibly enemy status or getting there. If they're in green they don't do it autonomously.

I'm a bit unsure if it shows in the menu until their score allows for it, but I have seen the options.

Yes, they fight if their relationship is low enough. I've had two children fight in my custom hood with all EPs installed. They just need a low relationship.

I think i have too many global behaviors that might have replaced the action.
Is there a mod that could possibly enable it, like Squinges mod fight anywhere.

More info on that here https://modthesims.info/m/showthread.php?t=639503 . I ended up sticking with the two Squinge fight mods I mentioned, so no idea how to get kids to brawl and still have the outcome be logical for all fights involving all ages.

Thanks, from what I've understood, the mods remove the actions rather than preserving the Child VS child fights.
Perhaps there's a way to modify it to bring it back.