Snowmen using pulled apart cotton wool balls, either stuck on paper in the shape of a snowman (they can choose whether to have a two part or 3 part body etc) and pre-cut (by you) hat shapes, eyes, noses etc for decoration, or you can use a cardboard tube, from the inside of napkins or wrapping paper for example, and stick the cotton wool around that to make a 3D snowman.
I've also seen angels made using cardboard tubes - pre-cut wings, coloured/glittered/decorated and then glued on, paper doilies glued around the tube to make her 'dress', and a face drawn on. You can use wool scraps for hair as well.