The IRS has $118 million to give out, but more than 200,000 checks have come back undelivered.
IRS Commissioner Mark Everson says all the agency needs is a good address, and the checks will be on their way.
The IRS has nearly 116,000 undelivered child credit checks worth more than $50 million, at as much as $400 per child. There are also 92,000 tax refund checks that came back undelivered, worth an average $722.
Taxpayers can use the IRS Web site to check the status of their checks and get instructions for claiming an undelivered refund.