Can I sue for identity theft on behalf of myself and my child?

I've recently found out that my soon-to-be ex husband filed fraudulent tax returns 3 years in a row, one of which the IRS is asking compensation for from me. My divorce has been dragging out for over 2 years. I have 4 children, 2 are biologically his. An order for child support was put in place on June 1, 2012. He has never paid, ever. The order also states that if he delinquent in support by 30 days, he is not allowed to claim our dependents for taxes. Not only did he claim them but also another one of my daughters and myself as well. We have not resided in the same county for over 4 years. I have been working with the IRS, and filed identity theft. I did not sign these returns. I found out that this has occurred for 3 years and that the IRS is seeking compensation from me for one of the returns he filed. I knew nothing about these returns until my returns were being rejected. I've been going to the local IRS office for help and I almost failed out of nursing school because they could not process my financial aid due to my tax situation. He has received over 18k fraudulently and has never sent a dime to his kids. After the IRS completes their investigation, do I have grounds to sue him? Do my daughters have any legal rights for their identity being used fraudulently? As previously stated, one of the dependents claimed is not biologically his and is not part of our divorce proceedings.