You would be single with a dependent unless your grandson was under the age of 24 at the end of 2016 and a full-time student for part of the year (or permanently and totally disabled). Then you could qualify for Head of Household.
Here are the requirements to claim a dependent:
Yes, you may
be able to claim your nephew as a Qualifying Relative dependent if:
• You provided more than half
of their support.
• Your grandson made less
than $4,050 in gross taxable income. (Social Security income generally doesn’t
count here.)
• Your grandson lives with
you (365 days in the
year) or they are related to you.
• Your grandson isn't a dependent
on someone else’s taxes.
• He isn't doing their taxes
with a spouse (married filing jointly).
• Your grandson is a U.S.
citizen, resident alien, national, or a Canadian or Mexican resident.
You can’t claim a dependent if
you yourself are a dependent on someone else’s taxes
