Did you already e-file? If you already e-filed, you have to wait for the return to be fully processed. Then you can amend to add the other child. You will need a special form called a 1040X which will not be available until later in February.
Wait until your original return has been fully processed before you amend, and make sure you have saved a pdf of the original return before you amend.
See this TurboTax support FAQ for amending a tax return - https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-change-correct-return-a...
Do not expect quick results from amending. It can take four months or more for the IRS to process an amended return.
You can watch for information here:
https://www.irs.gov/Filing/Individuals/Amended-Returns-(Form-1040-X)/Wheres-My-Amended-Return-1
**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.**
