Iced picture biscuits.

Grab a packet of arrowroots or similar, slap some coloured icing on them, and then using lollies and coloured icing tubes, draw little pictures. Red smarties for holly, you can get away with doing a single holly leaf. Or little triangular Christmas trees with some silver cachous for ornaments, little square parcels, etc. This usually takes a little while but it's always FUN and the kids LOVE them!!