I had just the opposite scenario one year, the IRS sent me a larger than expected refund with a letter letting me know that I should have claimed Head of Household rather than Single. While on the phone with the kind woman at the IRS, I asked her how I could get more children that I didn't have to carry for nine months, deliver, or support in anyway. She thought I was being ridiculous when I asked for the alleged SS number of this other dependent I was claiming and where that was on my forms as I didn't recall supplying any such information.

Silly me, I should have just kept the money and kept quiet. Being honest was actually quite difficult, it took a lot of convincing for them to go back and re-check their data entry.