How about a quilt for their classroom where they each bring in a piece of old clothing and then help you cut an 8" square, then you sew them together (they help with layout) then they help you layer and they tie it? There are some great children's books that would tie in to this; there is one about a little African American girl who makes this exact quilt out of family clothes as a gift (maybe tribute?) to a grandparent. You'll need to bring in some fusible interfacing for the tshirts youll get but otherwise you should be fine...and this can be completed in a day with you as the "Guest Artist"!!! (Yes, I've done this before!)