It may be that your grandson didn't meet one of the requirements needed in order to claim this credit.
To count as a qualifying child for EIC, your child/dependent must have a valid Social Security number (not an ITIN) and also meet all of the following:
- Be your child (including legally adopted), stepchild, foster child, sibling, half-sibling, step-sibling, or a descendant of any of them (for example, your grandchild or niece); and
- Be permanently and totally disabled OR under the age of 19 as of December 31, 2016 (under 24 if a full-time student) and younger than you (or your spouse, if filing jointly); and
- Have lived with you (or your spouse, if filing jointly) for more than half the year; and
- Not file jointly with their spouse unless they weren't required to file but did so anyway to claim a tax refund.
Another reason could be that you did not qualify for the credit based on income or another factor. Please see this link that explains the qualifications for the Earned Income Credit: https://ttlc.intuit.com/replies/3299933
