When somebody messes with, bothers, or pokes fun at the person that they like in order to get their attention or a reaction out of them. Derived from how young children call their crush silly names or annoy them.
Jonah: Why does Ed keep messing with Aalia?
Ale: Oh, it’s the kindergarten rule. He messes with her to get her attention
Jonah: *pokes Ale*
i’ll show you mine if you show me yours first
boy: “you wanna trade pics?”
girl : “kindergarten rules?”
boy: “bet”