For children:
Hand print pictures (many hands make a tree, two in brown can make antlers plus a rednose-thumbprint) that kind of thing.
Get a large piece of paper - if possible, use the 'wrong' side of an extremely cheap roll of wallpaper. Lay down child, draw around child, they colour in as they like, cut it out and stick.on their door. It should look like a gingerbread man.
Little bits of card cut out to make a fridgesnowman: roughly-cut round black.circles for coal eyes and mouth, orange card carrot for the nose, 3-4 more black circles for buttons going down the middle of your fridge. It looked really nice last year, possibly because I'd cleared all the crap - calendars, taxi numbers, reminders etc etc - off so it was clear and simple!
Pine cones dipped in.glue and rolled in glitter.
Big piece of card twigs and pebbly shit leaves picked up on a walk in the woods, make into a Christmas tree collage.