We live in a little cul-de-sac of 8 houses, and my children have become quite close friends with my 3 doors down neighbour's children.
The kids usually play out the front together, in my house, or in her house. Yesterday I had 3 (2 boys, 1 girl) of her kids in my house from around 5ish.
It was getting on for dinner time, so I was pottering in the kitchen, getting dinner ready when one of her sons hit my youngest (a proper hit, not squabbly pushing/shoving). I had words and told him if it happened again, he'd have to go home.
Then, I went out into the garden to give the veggie peelings to my kids guinea pigs. While I was out there, I moved their run into a new patch of garden, topped up their hay, water, etc, so I was a good few minutes. Came back in to find him sat on my kitchen worktop stuffing biscuits into his face that he'd raided from the cupboards. Took the biscuits away and made him get down. Had a few more words (I don't mind him having the biscuits per se, it's just that a) I expect him to ask first and not raid my cupboards, and b) it was getting on for dinner time so didn't think his mum would want him back stuffed full of biscuits).
He wandered off back outside, where my youngest and my neighbour's youngest were playing, next thing he thumps his younger sister in the small of the back - it was a good old whack, I heard it from the kitchen, so I sent him home
It's now ended up in a huge row with my neighbour as it's not "my place" to discipline him
She does have problems with her son (she has 4 kids, 2 boys, 2 girls - he's the youngest boy, 2nd oldest child). He's very aggressive, argumentative and rude and she does her best with him. I find him a complete handful, but he's welcome to come and play as long as he behaves himself but I'm not prepared to put up with his aggression.
As far as I see it, it's my house, and if he can't behave himself in it, I have every right to send him home