"In ProSeries it looks like they got the credit for the baby but that was for the child they could not claim this year."

It might help to understand how to think of it properly.

They got an advanced payment for EIP #3 against a projection that they would be claiming 1 qualifying child on their 2021 tax return.

You are now reconciling what they qualify for, on that return, with what they got, for the year of that return.