Hello, I went through the same issue with my ex, unfortunately there’s nothing you can do when it comes to the IRS. However if it is in your divorce and child agreement you may still be able to take her to court. As the decree is a legal and court agreement if either one of you go against it you are breaking the court agreement which is a violation with the court and could lead to severe punishment if it continues. File with the court that your ex is in violation with the court agreement you have, the judge will then set forth his judgment and could possibly make it so you can claim both children one year and/or make it so if it happens again it will result in a felony.
