My sister has had a couple of relationships like this, she's unfortunately still in one... I dunno how, but she attracts some hum-dingers...
Anyway, these are all the things I've seen from my sisters' relationships. But the first thing you need to think of, is your kids. They are the number one priority. Imagine growing up in a household with a violent and bad-tempered father. That is their home, the environment that is supposed to be their safety-zone.
Then you need to think of yourself. Is this the life you saw yourself living, the person you imagined spending your life with? Are you happy? Do you feel safe? You deserve more than this, and you need to have the respect and power within yourself to just stand up and say no, once and for all. It's an awful trap and circle to fall in to, since you may occasionally see things get better. They will apologise for their behaviour, they will be sorry - they are scared, as are you.
The same pattern happens with my sister. He's a nice guy, when he isn't angry. They'll have colossal arguements, he'll call her a fat-****, threaten with knives... then they'll stop and talk about it, he'll calm down and apologise in tears... then literally days later the same will happen. He's even squared up to me before when I asked him to leave the house, and he's a built guy... But she still took him on, even after that. Two years on, it's still the same for them.
I, along everyone else no doubt, urge you to leave. They may be sorry, but they will not change. I advise you find a family member/close friend that will help you and let you stay with them for a while. Perhaps take the kids over first, then confront your partner. The strength is inside you (cheesy as it sounds), but it's up to you to let it out. You are fully capable to protect your kids and yourself, just be aware of what needs to be done to do it. Good luck.