Once you leave your children, unless you have a lot of money there's no way you will be able to get residency of the children unless he is clearly directly abusive of them. I bet he will play it as you having deserted the children.
You will lose child benefit and any child related benefits (no matter how meagre)
You'll be paying child maintenance and you bet he will claim it against you (going by your description of their father) I believe the amount is 20% of your salary plus fees to the child maintenance company.
What makes you think he wont transfer his anger to the children, i.e. overly criticising them, bath mouthing you to them, telling them every time they put a foot wrong it's because you are their mother, having unrealistic expectations of them, setting them up to fail so he take his anger out on them by shouting at them or whatever.
Do you expect any contact with your children, if so how do you think you will go about getting it if he refuses to comply?
Leave if you want, don't justify leaving your children as 'the best thing for them'. It's not.
That's just for starters.