Talk

It's not up to you whether or not he brings his other children with him to visitation/contact. It's good that your LO has a relationship with his half siblings and it's not your place to put any restrictions on this when your ex is having contact time.

How often does your LO's dad see him?

You can't dictate to him when he can see his other kids, that's none of your business, it's nice that your lo has a relationship with his half siblings and has someone to play with.

Surely he is the main carer when you are not there? Regardless of whether he has his other children with him or not.....

i know quality time on a one to one basis is best for the dc, but its not always possible. Surely its not a bad thing that he is caring for all his dc at the same time?

he probably talks about his siblings all the time as they are fun and he looks up to them. When my nephew, who is 3 comes over he is all over my two dc! pretty sure he goes home talking about them a lot and not dh and I.

TBH, in my experience your DS is better off long term with a relationship with his siblings than his father. Men move on but kids who've got a relationship don't if that relationship is supported

What your child's other parent does with his child on his time is not your business . As long as he isn't abusive then how he parents is up to him.

I don't think you would appreciate being told by him who you should and shouldn't see while you are with your child.

Unless you are a
First or only child, not many of us have EVER had a parent 'to ourselves ' . I don't think most of the population of second and subsequent children have been damaged because of this.
Leave the man alone to get on with his parenting.

His father is actually doing the right thing. A sibling half or otherwise can be the support your child needs even if his father moves on.
That being said your child's contact with his father is no business of yours. If he is safe and not in danger his father can do anything he wants with him.
What he will be seeing is that dad wants him to know his other family.
So as harsh as it is. Butt out and let him enjoy the contact however he wishes to do so. You have no say in it as long as your son is not in any sort of danger.