Yes, you definitely should. File a 1040-X to claim make the return Married Filing Jointly and with your son as a dependent. It may be give you an additional refund for 2007 and will make them eligible for the stimulus as well. I don't know if you will get the stimulus automatically this year. If not, you will get their contribution to the stimulus next year when you do your taxes since there is a stimulus reconciliation in next year's taxes to make sure everybody got what they should have.