So I used to bully a kid in kindergarten. I don't remember what I was doing at all or the kid even, but I do remember his dad confronting me in front of everyone.
He didn't do anything mean, never raised his voice, all he did was calmly and repeatedly ask me why I was doing it and how it wasn't nice and all that. Just a straight talking to. I never bullied anyone after that.
Kids are scared shitless of adults they don't know, you don't even have to scold them or be mean or anything.
That being said, how the school is handling it is the bigger problem here.