This.
You can only raise the point that your child is saying they are distressed at what is going on in class and doesn't necessarily fully understand why it's happening.
You could say you are concerned at the normalisation of incidents in the class which are causing your son distress.
But unless you were a witness OR your son is able to verbalise what's happening when asked by teachers you are going to struggle.
We've had ongoing issues with a child in DSs class. We have witnessed various things outside school as well as concerns that DS has raised. There was also bullying and coercive behaviour going on which we were able to unpick and give evidence for. DS is yr3 and has been verbalising to teachers - this is unusual - several of his peers have had incidents but aren't mature or articulate enough to verbalise yet. I don't know how I'd feel if he wasn't at this point as several of the other more vulnerable children have been shafted by this reality.
We also had one incident where DS was told off for restraining another child. We questioned this, saying where did DS learn to restrain a child from hurting a friend and why was he ever put in this position when he had just reported a problem to the teacher and been told to just go back and play.
You have to be mindful of what schools can do - they can't act on he said / she said incidents. They have to have a witness willing to report.
You can only report what is affecting your child indirectly if you can't get them to otherwise articulate what's happening.
Ftw the other child in DSs class NEEDS retraining at times. I've seen first hand what he does and how violent / aggressive he is. It's an ongoing mess with safeguarding v SEN v difficult parents. DS seems ok at moment after we made a stink about the impact on him.