If your son was living with his dad (not sure I completely understand the back story), then the dad should be the one claiming him as a dependent. Really, your taxes should be filed independently of your adult daughter. Y As far as the child support issue goes, that needs to be handled through your lawyers, not through the tax system. You've gotten your daughter caught up in the financial battle between you and your husband which is really not fair to her and I would guess it is painful for her to be stuck in the middle this way. It is probably important at this point in your adult childrens' lives that there be a financial boundary between all of you to lessen these kinds of complications.