look on Line 30 of Form 1040 - they money should be listed there; that assumes you correctly added your newborn as a dependent and when asked about the two stimulus payments, respond with what you ACTUALLY received, not what you expected to receive
the same thing will occur next year for the 3rd stimulus.. presumably you won't get that now (because you have not filed 2020 and the IRS doesn't know about the newborn). That will settle up on Line 30 next year.
ps your son is also eligible for the 1st stimulus so expect to see $1100 on Line 30 as it's based on your dependents as of 12/31/2020, not who was alive on the date the payments were made. (I always found it humorous that the 1st stimulus was signed into law in late March which means some were not even conceived when the law was passed but their parents get the first stimulus of $500 for them if they were born by 12/31/20! )
