How do I sue my abusive husband?

So we had a divorce 3 months ago and the custody of the children is mine. He keeps insisting that the kids should be with him because he claims that I’m a terrible mother who’s careless about her looks. I’m not in anyway offended by what he said because it was his decision to marry me, but what happened was basically, he just cheated on me with his 2 mistresses.

I don’t trust him to take care of the kids because he’s also abused me for years, he hits me with a mop and throws water at me when I wasn’t able to cook for dinner. Right now, he just assaulted our 4 year old daughter and our 6 year old son is scared to see his father because of his actions. As a single mom (29F), I know my responsibilities for my kids and I don’t want my husband (35M) near our kids because all of us are scared on what he might do furthermore. How do I file a case against him?
How do I sue my abusive husband?
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