if you claimed your baby on your 2021 tax return, then the stimulus due to you should have appeared on Line 30 of Form 1040.
The Recovery Rebate Credit on Line 30 is $1400 times the number of people listed on your tax return LESS the money your received in March-- May, 2021
1-what is on line 30?
2- what is on Line 28 of firm 1040? Did you receive the $3600 child tax credit for Baby?
note regardless of when Baby was born during the year you were to answer that Baby lived with you 'all year'.
there are a few exceptions to these rules which i will not get into now......