If your son filed already and did not indicate that he qualifies as your dependent, you will not be able to claim him on an e-filed return. Instead you will need to print your return and file it by mail. You son will need to amend his return in order to "un-claim" himself. When IRS receives your return, they will send you both a letter and may request additional information. The other way around this is to wait until your son's amended return is fully processed (it can take up to 6 weeks), then file your return (still by mail). If you choose this option, you should file an extension for your own return.
