Courts will probably give you full custody if your ex puts your child in harm's way. You have every right to protect your child, I would go to court to block her from spending any time with your child. Good luck, let me know how it goes.

Yes, and you answered it what is best for your children. Yes you can take him to court if the courts new that she was there and she has been convicted of child abuse then there is no way the court would let tehm go there and he might end up with supervised visits.
No it is not wrong there would be no way in hell I would let my son go near anyone if I new they were convicted child abusers. You are doing what is right for your children. Eventhough you may feel as though you dont want to keep them from there dad becasue they have that right too but If he cared about it then why would he be with a child abuser. You are doing the right thing you are your childrens advocates so you need to stand up for them take his butt to court. If you do not have legal custody yet then go get physical soul custody now becasue with her being there with him it would be a good time and it would be as hard. If there is no legal custody established becarful becasue in MI whatever parents have the child can keep the child if there is no legal order. Then if the other party tries to go for custody then the child stays with you ever that child was with. Basically you can keep them from one another until custody is established. Call the courts