You new baby does not go on your 2020 return.  The new higher Child Tax Credit is for 2021 anyway.  

New 2021 3rd Stimulus payment, Unemployment and Child Tax Credit

https://ttlc.intuit.com/community/tax-topics/help/how-will-the-stimulus-package-impact-me/00/1393859

The new Child Tax Credit is for 2021, next year, when  you file 2021 tax.    It also raises the cut off age from 17 to 18 and makes the credit $3,600 for a child under age 6.

the IRS says it is working on a plan to allow taxpayers with children born in 2021 to report this fact so they get the advance payments.  

it's not ready yet

you may want to periodically check this page for update

https://www.irs.gov/credits-deductions/advance-child-tax-credit-payments-in-2021