Use impressed printing techniques to design and print your own Christmas cards.
Get the kids to create a drawn design for a card, keep it simple.
Then, when they are satisfied with their designs, re draw them onto thin sheets of polystyrene.
You can purchase commercial "press print" or use recycled polystyrene sheeting.
An ordinary pencil can be used to draw/make impressions into the polystyrene.
Make sure that the lines/impressions are fairly deep.
These sheets then become their printing blocks.
Roll water based printing inks over them and press onto paper to create your prints.
The blocks can be used over and over again to create multiple prints of any image.
The blocks can also be washed, dried and re-used.
Experiment first with one colour (white ink on black paper is very effective).
Thereafter experiment with adding other colours and with mixing colour.