Stonebirds,
Talking to such a man won't work because he won't listen but will likely shout you down instead.
He has now slapped your DD twice and continues to mistreat you all. Your 3 year old escapes currently purely because she is not old enough to answer back.
You are by turn allowing your children to be abused by their Dad here; you condone it. Sorry but you are allowing this currently.
If you want a relationship with your children as adults then you need to all get away from your H now. Make plans to leave him, line up all your ducks in a row first off because such men do not let go of their victims easily.
I'll tell you something else about the children as well. Your children as adults won't thank you for staying with such a man and could as adults rightly accuse you of putting him before them and or being too weak to leave. This could well happen even if they bother to speak to you by then and not completely despise you. Is that what you ultimately want?.
Look again at what you have written below. You have become completely conditioned to being abused, all your words indicate as much.
"Cestlavie ? my youngest won?t start fulltime school till September. But I agree I could work. I won?t earn that much though
"The thing is I love my home, neighbours, life apart from this. I?m worried what will be round the corner if I split with him. I?m not that hotheaded so I have to really build up to a decision like this. And I always think of reasons to put it off ? for example, till my youngest starts reception and I can work. And as he?s not around a lot of the time, I forget about it and carry on until the next incident".
Stop making excuses for either yourself or your H. He is of no consequence here.
Do you really want to live within a broken home/family unit because its already fractured now. A house physically is but bricks and mortar.
What will it take for you to actually leave; hasn't he caused enough damage to you all already?. Your last sentence within this is precisely why he has been allowed to continue; you've allowed him to - and also because he can.
Re this comment also:-
"I could give him until September and maybe make a list of ways in which I want him to change. What does everyone think? But I keep coming back to the way he treats DS. I?m not convinced that will change".
No he won't change; he will only become even more abusive towards you all. Stonebirds next September is far too bloody late; he will further destroy you all by then. Your DS and DD are being emotionally abused at his hands.
You did not answer my question put to you earlier either which is what do you get out of this relationship now?.
You have a choice re this man - your children do not.