AIBU to worry about my stepson's aggression towards the younger children?

Good points.

@Wafflecakes does his Mum have a partner too and/ or other children?

This is what I think would be the absolute shit sandwich.

Obviously no one should say one parent can move on to a new relationship and the other can’t, but it must be god awful if they both do

She’s explained how he is at school, he’s bullying other kids, and he’s violent at football. By all means read all of her posts while sticking the boot in to her, apparently the only adult in this boy’s life who cares about his behaviour.

Surely this isnt new behaviour youve had six years together he doesnt like other kids especially kids that live with his dad. Regardless if he was a product of a one night stand you then decided to add another child into the mix with your additional two. So yes this was selfish behaviour.

you've been around this child almost his entire life when did this behaviour start?

Agree. A child that young isnt acting like that because they are inherently bad. But clearly something is going on with him. It might be insecurity about the situation, it could be that he is being bullied at school, it could be something else going on in his life. Best case scenario he is just looking for boundaries and not finding them but I do think the dad should be more concerned with his son's well being. If my child had a limp I wouldn't look for excuses for the limp or deny it existed. That would be a form of neglect. So is ignoring a child's behavioural issues.

I’m not sticking the boot in her, I’m trying to demonstrate how awful this life would seem to me if I were him and recommending a solution (that doesn’t involve her.)

Do you have constructive alternative ideas?

Its not the stepmum part which is the problem. You sound like a compassionate and concerned stepmum.

Its the lack of a settled environment, having to share (things, money, space, attention) with a lot of other children. Its the sense of never being at the top of anyone’s priority list.

I agree with others that your DH needs to really step into this. He’s not taking it nearly seriously enough.

Usually I give an example of one of the posters who wrote about their Chinese or suchlike grandmother dealing with her aggressive little brother, but in this case all I can say is 'that poor boy, that poor boy whose father wrecked his young life by shacking up with a new woman and immersing himself in a new family'. Nothing else to say, really.

Again your mimising the impact you and your children have on this boy not all children like blending famiies with strange children they dont get a choice to be with. Its not the same as growing up with a sibling from birth. You have a duty of care to your dc to protect them. All the children have been failed.

From what you have said, I feel he is being let down by ineffective parenting and a lack of consequences for his behaviour - from both his parents.

Big emotions indeed.

Ideally his parents and step-parents need to get together and work out a unified way of reacting when he behaves badly. You all need to be on the same page, so he knows where he stands.

Obviously in any family a child can have ADHD, but research indicates that children exposed to severe family disruption, trauma, (like divorce or domestic instability) are more frequently diagnosed with ADHD.
Trauma and chronic stress in the home can cause behavioral problems, trouble learning, and high activity levels. These stress responses often look identical to ADHD or can make underlying symptoms much harder to manage. Sometimes, trauma-related distress is misdiagnosed as ADHD.
There's articles from the Times and many studies on this.

You have a husband problem

Ok op, if you cannot see that it is your husband who is the problem, then steps until you work it out are…

your older two go to their dads on the same weekend as he comes

you take your 3yo dd somewhere for the weekend every time

Your children don’t have to be inherently annoying to be annoying to him!

Sounds like it might be an idea for the eow that you kids spend with their dad to the the weekend your DSS spends with you though. That should lessen the impact on everyone.

You may well have thought of that already but it’s not clear.

There could also be trauma going on somewhere else altogether like at school but your DH does need to get his act together and start trying to get to the bottom of things. Ultimately it’s on him to do it!

What would you like to see happen here OP? What do you think will help?

Interesting that he targets the girls. You need to do a bit of detective work about what sort of environment he has around him at his mother's - or rather your partner needs to sort this out.

It sounds as though he's absorbing some nasty misogyny from somewhere.

I think his mum and dad need to sort him out and you need to protect your own children. He needs to see a counsellor, and his dad need to get his head out his ass in regards to his son showing obvious signs of distress. It’s alright now while he’s young and it’s easier to manage him physically, but boys grow and they grow fast. Tell his dad he needs to collaborate with his ex, get his son the help he needs or you and your kids are moving out.

My son is a similar age and the aggression he comes across at football, both playing and watching games, can be considerable.

If their dad/son bond is quite football heavy, it may be that this is how he thinks his dad wants him to act. No consequences would back this up.

Your SS is being failed by both his parents. Your DH for not dealing with his son's aggression with consequences, and his DM for her gentle parenting approach. He is also learning aggressive behaviour from playing violent video games and could be experiencing it in other areas - school, football, friendship groups, TikTok etc. You can't do much about his mum, but your DH needs to step up and his son needs to see a counsellor. If he refuses, and continues to put his DD at risk from his son, then it's up to you to take action by separating from him. Be forthright with him that that may be the consequence if he keeps burying his head in the sand.

Your partner is a shit dad to all his kids.
He doesn't get a medal for bringing his child to football and booking a trip to Portugal with his son, while you are left at home with all the other kids.
He's having a great time for himself isn't he