The easiest Christmas card crafts are generally the simplest. You need a sheet of paper and some construction paper for each student. One red sheet, one green sheet per student and assorted colors for a group.
The construction paper should be slightly larger than the single white sheet. Fold them both in half and paste the white sheet on the inside to form the inside of the card.
Then have your students write a personalized message inside the card.
Next, decorate the outside cover. Be sure that the card is not upside down! They can draw a picture, cut out shapes from the other sheets of construction paper and paste those on. However they want to decorate their card is fine.
Then you're done!
You can also print some free cards with Christmas images to color for the cover. There are many printable card sites out there. However that doesn't really inspire creativity.
In any case, I hope that your students enjoy the activity!