Child must not have checked the box that says he can be claimed on someone else's return. Yes child needs to amend. But the parent will have to mail their return this year so they don't have to wait. Once a ssn has been used you can't efile it again.
How to Amend an Online return,
https://ttlc.intuit.com/community/amending/help/how-do-i-amend-my-turbotax-online-return/00/27577
How to mail a return from the Online version
https://ttlc.intuit.com/community/printing/help/how-do-i-print-and-mail-my-return-in-turbotax-online...
Be sure to attach copies of your W2s and any 1099s that have withholding on them. You have to mail federal and state in separate envelopes because they go to different places. Get a tracking number from the post office when you mail them for proof of filing.
