She practices her counting with the cups and we have a great time. My 18 month old is usually providing the music for us by banging on the pots and pans. Give your children specific tasks. Such as when people come over for the holidays make one child's job to take the coats and place them in a specific place. Another child might set the table or make sure the centerpiece is in place.
Kids can write their own cards.
I have my children place their handprints on the cards since they can't write. People love this and it makes the kids more a part of the card process. I try to let the kids help me pick out gifts. Let kids make their own gifts. For grandparents far away let the kids tape-record themselves singing a Christmas song or telling a story.