You would have to print and mail your tax return if you'd like to claim a child that has already been claimed. Please attach a statement explaining why you are mailing and submit any proof that you may have showing that you are custodial parent and that you should/can claim the child. The IRS will "examine" your proof (such as medical records, school records, any bills that show that child has lived with your longer) and will decide who can claim the child. The IRS most often gives the dependency to the custodial parent (parent with whom the child live longer during the year).
