keeping children safe in a divorce

In a marriage where the husband is unsaved and is abusive to both his wife and their children ( verbally and  scares and sometimes spanks the children too hard), how can the wife get a divorce considering it will be even worse on her children when they go for times of visitation with their father? I have spoken to mothers in this situation and they say that as long as they don't leave (divorce) their husbands, they are much better able to protect their children. But if they do divorce, the unsaved husband, having poor judgment and meanness/ungodliness, can be free to abuse his children more and can bring others of unquestionable character around the children. A good or godly mother's instinct is to protect her children always. This is truly a catch 22 type of situation, so what can a mother in this situation possibly do? Do you think she should give up her freedom by remaining in the marriage for the sake of the children? Of course, only God can lead her, but wondering if anyone has known of someone in this situation and how she resolved it?

jane