Are you saying you already filed tax returns with Child Tax Credit, without finding out about the advance payments? Or that you filed them based on the deposits in their accounts without seeing what the letters said?

There have been news articles where the IRS admitted a bunch of the letters were wrong and suggested the taxpayer set up an IRS account and double check that way for the ACTC information. 

I had not done many yet, but I was kind of under the impression that IRS was matching the amount sent as ACTC to the 8812 as filed. But maybe they are not doing it fast enough to reject the return, but will be checking before processing refunds.