You can both amend now if you want to and if you are positive the "kid" cannot be claimed as a dependent. The rule is if they CAN be claimed as a dependent then their return has to say they can be claimed:
https://ttlc.intuit.com/community/dependents/help/when-do-i-have-to-answer-yes-to-being-claimed-as-a...
Do not expect quick results if you amend. It is taking the IRS more than the "normal" four months to process amended returns. Expect it to take at least six months and be pleasantly surprised if it takes less time.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
