Unfortunately Turbotax cannot tell you if anyone claimed your grandson on their tax return, nor will the IRS tell you if anyone claimed him.  The only way you would find out is to try and efile a tax return with your grandson being claimed as a dependent and then the efile being rejected by the IRS because his social security number, (SSN) was already used on another tax return.  In that event, the person who could rightfully claim your grandson as their dependent, would still be able to include him on their tax return, but could not efile the return because as I stated above, it would be rejected by the IRS.  Instead, they would have to paper-file their 2016 tax return. To do this, you would select Paper-File instead of Efile when you are in the File section after completing your return. Then print, sign, date and mail your tax return by April 18, 2017.