I have never heard of a stimulus check marked child support! In fact, I specifically asked the IRS if they were withholding from those who owed back child support and handing it over to the deserving parent who should have received it, and my IRS contact said that would be up to the estate.
I’m going to say something that just comes from the heart — and can’t guarantee that they won’t come back to you. But I would deposit the check in the estate, and worry about them coming back to you later. They are still trying to get money OUT to people who really need it. I don’t think they are going to track down these payments to the deceased, much less one marked child support!
And if they ultimately do start trying to find those checks, they will run up against a lot of pushback from legal advocates who say the law specifically does not allow for recoupment, and that the law specifically says anyone who filed a 2018 or 2019 return is entitled to payment!
So we will see, and I can’t promise anything, but Iwouldn’tlose sleep over it!