[galaktor]

You're assuming she didn't want to be kissed (we don't have the girl's perspective on this; apparently they're "boyfriend and girlfriend", which I don't think are valid terms with six-year-olds anyway...).

Expelling imho is very extreme in this case, there's other ways to communicate to the boy/class that it wasn't appropriate without making a way-to-public statement about it.

[sp332]

He wasn't expelled, he was suspended for one day. With so little context I can't say much else.