You should claim the children yourself. If the IRS checks they will then write to you both asking for explanations and proof. At that point you ex will be in deep doo-doo. If you are really sure about your knowledge you can report him to the IRS for tax fraud now.

If your ex has not been paying for child support.you should be getting back his incom tax refunds until he is caught up on his errors. You just need to file a motionagainst him for contempt of court,one he is in contempt not only for the child support but because he went against the court by claiming the kids on his incom tax. So I would first sujest that you file a motion against,that will also help you to be able to get the court to enforce the child support. They can do several things to make him pay,he could lose his drivers licence,or have suspened until he starts paying,he could also be sitting his butt in jail awhile,his wages can be garnished and again you are entited to get his refund checks. You can legally claim the children so just claim them,and if and when the IRA finds out that you both claimed them they will notifly the both of you,and as long as you have proof showing that he is not to claim the children then they will go after him to repay the money back. So it is up to you to decide if you want to report him or just wait until the IRA finds out and sends you both a letter. Personnay I would just file against him for contempt and get him to start paying his child support and let the judge know that he is claiming. Use your best judgement on this,but remember the court can help you. Good luck

Go head and claim your children.
File for unpaying child support.
It's very important that it's says in your divorce decree/child support. This way he will be responsible, not you.

I just went through this. I received a notice from the IRS that said someone tried to claim my daughter after I claimed her. Even if you had joint custody you would have to sign a form every other year allowing him to claim your children.

Write the IRS and explain the situation. If you have court documents showing you are the primary and sole custodian they can review his tax file and stop him from filing.

I showed that I have full physical custody, he only has her 20% of the time (if that) and the divorce decree showing that I get to claim her every year. They wrote me back and said no action will be taken on my taxes and I was ok to claim her yearly.

I have had my ex husband do this to me several years. I've have aproched it the same way each time and its come to bit him latter on. If i file elctonicly and it gets kicked back because my son has been claimed i then turn in my IRS form through the paper means. I mail it in and i know it takes longer but I get my full dedutions and check for my son. Then the IRS catches it the send each of us a letter and i mail in the copy of the divorce degree and he ends up having to pay the IRS back.

Its a pain and takes longer but i still get my full amount. Lucky for me my ex does not play these games anymore becase they where getting very expensive for him.