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

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

You have a husband problem

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.

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.

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.

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.

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.

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?

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.

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

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.

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.

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

I would probably feel aggressive too if I had to put up with a blended family, an adult who wasn’t my mum taking my dad’s attention and her two annoying kids PLUS a baby who is no doubt apple of their eyes and replacing me in my dad’s time and affection.

What a sh*t deal.

I think he needs extensive 1:1 time with his dad every weekend most importantly, and probably with his mum also while he’s there. He needs to feel like he is someone’s priority. There’s an awful lot that he can’t control going on here. How is he doing at school?

Why not take a step back from trying to fix your partner in to being a decent parent to his daughter, and think about why you are attracted and so defensive of a man who does nothing about his 3 year old daughter getting punched in the face.

I think it’s massively hard for kids to go and “stay” with their Dad (to use your word, rather than “lives with us eow”) in a house where other children live full time. And those other children presumably see you as just “staying with” them, whilst it’s their house.

I can’t really imagine how that must feel but it can’t be good.

Not those other children’s fault, but the adults involved, especially the parent they have in common, have to work extra hard to make sure the child feels equally at home and equally part of the family.

And he’s far too young for fortnight!

It’s slightly disturbing that his dad isn’t more concerned about sorting this out. He’s clearly
got an issue, to go from quiet and clingy to aggressive and lashing out at other children. Perhaps he’s being bullied, or worst case scenario - sexually abused. It needs looking into. Frame the conversation around concern for the boy, to prevent his dad going on the defensive.

You're having difficulty with the child that has to see other children live with his Dad, while he doesn't. He needs intervention, to help process his feelings, but your DH is failing him by not getting it. You seem obvious to how the child is interpreting the living arrangements.

You’ll get slated here by unhelpful handwringers purely because you’re a stepparent.

He needs to be told off. The problem is his guilt-driven dad.

Consequences? He needs to be told to behave properly.

Oh behave! The OP said his mum and dad have never been together. Is his father expected to stay single until his DS is 18?

None of that makes a scrap of difference. The current situation is not giving him what he needs.

He is a very unhappy little boy who is crying out for help.

Don't minimise the situation by trying to slap a label on it.