I thought of a few other things (walking the dogs, looking for the meteor showers does wonders)
do you sew?
when I quilted I would often use "strip piecing"
for a fun table runner or garland or something along that line you could cut your squares of fabric either out of your mom's leftovers (she would recognize them) or some colors she loves.
then sew diagonally through one square at a time without cutting the thread.
that way you would have as many little squares all sewn together on a strip like a banner.
You could use this going down the middle of the tables for a fun little runner, or if you are going to be haning any garland, use this instead.
For a keepsake for your mom, you could cut squares of off white / white fabric or shades of line (use cotton) and then ask the guests to either sign their name on a square, or write some funny, sweet, special memory of your mom. Afterwards you would collect the squares and maybe make a throw sized quilt. You can use strips of fabric your mom likes in between and just have simple blocks. Use fabric markers -- you can get fine point fabric pens in the sewing section (sharpies might run, you would have to pre-test those)
or if your family has it together, you could ask the family to do the same, before the big party, and present it to your mom at the party. (my family could not do this, even with lots of prodding)
Little ones could do their hand prints on the blocks of fabric
you can make any acrylic paint a fabric paint by adding a something (i cant think the name of it even though i use it all the time -- textile medium!~)
have the little ones rub dish detergent into their hands and wait a minute or two before rolling paint on their hands -- this helps the paint to wash off very easily)
okay, those are my ideas