My ex husband has joint custody Dcfs has been called 4 times that I know of for the same thing. The last time they were called the kids got taken away for a month, and he got 5 years probation. Y did theylet my kids back in the house with an abusive dad?

Have you asked "them"? We have no way of knowing.

Perhaps there wasn't sufficient evidence, perhaps he has changed his ways, maybe it's something else.

Why don't you have custody?