If you filed a 2020 return and claimed your child as a dependent, you already got the rebate added to your refund. (Note: the child must have a valid social security number before the filing deadline which was July 15, 2021 due to the pandemic.) Why didn't you claim your child as a dependent in 2020? Or did someone else claim the child? If someone else claimed the child, you can't also get a rebate, unless the IRS does an investigation and determines that the other person who claimed the child was wrong and you should be allowed to claim them.
Then again, for your 2021 tax return, if you claimed your child as a dependent, and had not already received a stimulus payment, you would have claimed the credit on your 2021 return--it was part of your refund, not a separate check. Why didn't you claim your child on your 2021 tax return? Did someone else claim the child?
Or are you saying that you never filed a return for those years?
Also note that, to claim any refund by amending a 2020 return (or filing a new return if you never originally filed), the return must be filed by July 15, 2024 or it will be considered too late to pay even if you qualify.
