To think Dsis is overeacting after SS hit niece?

I'm not sure winding up a teenager and pouring water on his drawings is considered cruel. If an adult did it then absolutely, but a child is playing a game to see how far she can go and is being allowed to torment him without being told off.
The 10yo has seen him getting wound up from minor things and has decided to wind him up some more. OP sat helplessly watching it unfold without intervening.
Both kids needed to be told off before it escalated. Once he hit her the opportunity is missed.

Again ALL in front of an adult

now imagine him alone with a teen girl. No adult around. And he gets worked up about something.

She should have stood up and intervened. I’ve breast fed 4 children, if my child was being taunted I would have stood up. Oh don’t mind little Jimmy being electrocuted, I was busy with the baby 😂She’s clearly exaggerating the nieces behaviour or a complete moron if she didn’t see it turning nasty.

Bizarre. I absolutely want to thoroughly instil in my children that deliberately winding up people, especially people with anger issues, is a terrible idea. Why would you not want your child to understand that? It’s not about teaching that some behaviours mean you deserve to be hit, it’s about encouraging common sense. In the same way I strongly encourage my children to be sensible around dogs, open water, traffic… people can be hazards too. I would be cross with my children if they deliberately wound up a dog, so I’ll be cross with them for winding up a person too.

It’s also clearly morally wrong to deliberately wind someone up who is trying to get away from you. It’s also stupid to be surprised when they then snap. I don’t want my children to be unpleasant or stupid, so would correct them accordingly.

I disagree with OP that they are equally in the wrong. Hitting is worse than words. It won’t be popular on MN, but I also think that boys should be strongly reprimanded for hitting girls in particular. But the fact that the SS did something worse doesn’t change that the girl’s behaviour was wrong too.

OP, get your SS some help, and tbh your sister and her family sound unpleasant so I’d give them a wide berth from now on anyway.

I think you sound lovely op. You clearly understand him and advocate for him well. Should he have hit a 10yo, well obviously not, but he's still a child himself, a traumatised one with additional challenges to face which he's getting help for and she's old enough to know to leave him alone when asked and that calling someone a crybaby is likely to get a reaction she might not like. Your dsis sounds like a cow telling you to put him into care.

Oh come on.....hurt? Just think you lose an argument as soon as you resort to that juvenile language. X

She is over reacting with social services and police threats. And she is wrong in telling her DD not to apology.

He has issues, but is working in them and getting better - he tried to remove himself from the situation.

It is clear that your sister and her DD aren't a safe environment for him - at the very least he needs to be able to get away from them when he needs so.
If you can't stop DN from following him, her mother needs to be there.
They should never be left alone together, and it seems that one adult with three children with so different needs (baby - feeding and holding, him - way out, niece - protection from her own stupidity/inability to respect boundaries) isn't enough.

Obviously both of the DC here are a product of their parenting and need intervention to undo that. I would tell your sister that you are happy to stay away as clearly she is deliberately raising a bully and you do not want your children around that. SS needs the love and support you are giving him, not abandoning.

No, absolutely not, he should walk away. Oh wait, he did!

Mumsnet isn’t for you if you’re going to get hurt by someone swearing in a post about a teen boy losing it with my teenager girl

which is very likely with this individual if he does this to a 10 year in the presence of an adult

Your sister is very unreasonable to mention police and SS. But a 15 year old shouldn’t be hitting a 10 year old girl either. He needs pulling up on that for sure. Don’t minimise it. And don’t go on holiday with your sister again, it sounds like she doesn’t consider him to be part of the family and the kids clearly can’t get along. Recipe for disaster. If you can get ss
to apologise then it might smooth things over for now but he probably needs help for his anger.

A rod no wider than the thumb 😁

I’m really surprised at all the people saying this is ‘normal 10 year old behaviour’. Is it? I have a 10 year old daughter and I would be appalled if she behaved like this! In fact my 8 year old (who could never be described as a gentle or particularly empathetic soul) wouldn’t dream of doing this either.

Obviously hitting her wasn’t the right thing to do and the OP has acknowledged that several times, but her niece wasn’t being ‘annoying’ she was being deliberately cruel and not allowing him to leave the situation.

Does she often behave like that towards emotionally vulnerable people @PapaSteel? Is your sister doing anything to address it? I think it sounds quite concerning and something that warrants some investigation.

Just read the thread

the vast vast majority are saying quite the opposite

It's a bit of an unholy mess. What are you most upset about? Your SS hitting neice, your neice's behaviour or your sister's reaction. All three are wrong. Why are you on holiday with your sister's family? Is this a first or just the first bust up.

For me there are 2 separate issues. The younger child’s behaviour, this needs to be addressed by her parents. Although violence can never be justified, she’s putting herself in harms way by deliberately goading an already angry young male.
The 15 year old, resorting to violence, needs better supervision especially when around younger family members.

It’s amazing how many people are minimising a 15 year old hitting a 10 year old. Yes she was winding him up but we live in a world where you get wound up and you have to be able to control yourself.

So many women are murdered by their husbands/ partners and sons. It’s so common it barely makes the news. Many many more are assaulted every single day. This is how is starts, minimising the violence because they were provoked.

To those who said she deserved it- how hard of a hit is acceptable? A red mark? Broken nose? Being knocked unconscious? How do you measure what level of attack is justified?

Winding someone up isn't as bad as thumping them, especially with this age difference. SS needs more support with managing his anger.

Nor myself or OP have once suggested it's OK - but thanks for swearing!

Don't be so bloody ridiculous. These situations are not comparable. There's a huge difference between minding your own business, while wearing a dress and deliberately goading/bullying another person.

How?

Honestly it feels like all the adults in this situation are failing all the kids in this situation. It comes across as they want to be their kids friends rather than their parents. T

Stop it! You’re being idiotic now.

For what it's worth this young man will most likely come across other nasty people that will get a kick out of provoking him for a reaction and will need strategies to cope. The walking away was the right thing and he needs to keep up with that as well as learning to tune people like that out when they say deliberately hurtful things.