Here is how to amend your return (How to File an Amended Tax Return with the IRS) "If you prepared your original tax return using TurboTax, log in to your account, open the tax return you already filed, and click on the link to amend your return. From there, the software will walk you through the process of filing the amendment."
As @xmasbaby0 mentioned, you will need to wait until the IRS accepts your return to make an amendment. If it happens to be rejected, you can simply make the updates to remove the child along with fixing what caused the rejection, and e-file again.
