that is the way it works.
for the 1st two payments, the IRS used 2019 (or 2018) to ESTIMATE what you were due and sent out the stimulus payments. An amendment doesn't change that estimate
Then, the 2020 tax return determines what you are ACTUALLY does.
If the ACTUAL is greater than that ESTIMATE, the difference is on Line 30
if the ESTIMATE is greater than the ACTUAL, you do not owe the difference and Line 30 is 0.
in your case, your child was not eligible on your 2020 tax return for the stimulus payment because he was 17 years old in 2020.
Now for the 3rd stimulus, what was just sent out was the ESTIMATE. The rules changed and 17 year old dependents are eligible. So your ESTIMATE based on your 2020 (or 2019) tax return is $1400. But the ACTUAL when you fill out your 2021 tax return is zero (because he will be 18 in 2021).
And again, since your ESTIMATE is greater than your ACTUAL, you will not be asked to return the money.
there is nothing due you for your son on the 1st two stimulus payments and on the 3rd the taxpayer gets the payment - not the dependent, so your some won't get anything (as long as he is a dependent on your 2021 tax return).
