Hey Megan, what a great idea for Christmas gifts! If I were doing a project like this, I would scope out sale yarn at my favorite yarn shop and purchase enough to make all the scarves. Then I would settle in with my size 13 or larger needles and do a pattern something like this...
Cast on 15 or 20
Garter stitch (knit every row) for 15 or 20 rows
Stockinette stitch (knit one row, purl one row) for 15 or 20 rows
Continue alternating between garter and stockinette to make sections roughly the same size but don't fret about a row or two difference
End with a garter stitch section when yarn is gone or scarf is long enough.
This works great with a yarn like Lion Brand Homespun
and you can get a good length scarf from one skein.
Doing the alternating sections of garter and stockinette makes it so that the edges won't curl up like what happens with just stockinette.
You'll have busy fingers until Christmas! Go for it!