My return was rejected. It says someone else is claiming my child. My ex says he put them down, but did not claim them?

[janelleseville]

We filed jointly till this year, so the kids are all on his information. I am claiming two this year, and he is claiming the third one.

[PatriciaR]

A dependent's SSN can only go through the e-file system once.  Please see below:

To prevent fraudulent returns, the IRS will only accept each dependent's SSN once in their e-file system. Because the other parent filed first and used your child’s SSN, no further e-files using that SSN will be accepted. 

 You will need to print, sign, and mail your tax return to the IRS.  Your tax return will be accepted if you paper file.

[janelleseville]

even though he put them as non dependents?

[macuser_22]

It depends on which parent the children physically lived with more than half of 2017.

[PatriciaR]

Right, because the dependents' SSN was on your ex-spouse's and went through the e-file system, you will not be able to e-file also.  You will need to mail your tax return.