mulranno, you didn't give details before, and I am shocked to hear that this has been going on for two years, and the details of his assaults. I am so sorry this is happening to you. It is domestic violence without a doubt...
You do not deserve this. You have a right to be safe. You are doing absolutely the right thing here by seeking outside help and involving the police.
Coming to get you when he wasn't even in the room and punching you to the floor deliberately is way, way beyond behaviour that might be forgiven after an apology, mulranno. What you describe is not an adolescent loss of temper; it is a serious assault.
I can't help feeling that there are two abusers here. If your husband had stood by and let this happen once or twice, it would be a terrible let-down and a breach of trust, but you could just about explain it away, thinking he was slow to act because he was shocked and in denial. But after two years it is far more than a let-down: it is a total betrayal. I can't help wondering whether he's actually pleased your son is attacking you - whether he's effectively getting your child to 'do his dirty work' for him... :( I'd tell you your marriage is over, but you already know. I am so sorry. :(
Is there any way you can take the other three children and leave? Do you have anywhere to go?
I imagine with three younger children, that would be very difficult - it probably feels impossible. I just want to check that you know about refuges, and the support provided by Women's Aid for women living with or escaping domestic violence. You can call them - they offer advice and support over the phone - or you could go to a refuge, which would be a huge upheaval for you, but might be better than the life you're living now. Children are badly affected by living with domestic violence, and two years is a long time, for them as well as you.
You have already triggered a child protection referral which means social services will check to see if there are any registered concerns about any of your children. They will see it as a good thing that you are seeking help. They are more worried about women who hide problems, because they know it is hard to ask for help if you are pretending everything is ok... and in circumstances where violence is a secret, women and children are more at risk. You're not pretending, so they know you're better able to keep yourself and your children safe.
If you can't leave or don't want to, you can ask the police and social services about removing your son and husband. You may not want to do this, but I want to be sure you know it could be an option.
You have said a couple of times that you are worried about things 'escalating' if your DS finds out you've told school and the police. I guess you mean you are afraid he may beat you up. From what you have said, he might. Don't take any chances. Call 999 if you have the merest suspicion that he might get violent.
In fact, call 999 any and every time he is violent or you are afraid he might be, from now on. You have a right to be safe and feel safe, mulranno.