Christmas Around the World by Emily Kelley, illustrated by Priscilla Kiedrowski (Carolrhoda Books, 1986).
I've always been a big fan of Christmas, as well as learning about other cultures' traditions. So I loved this book as a kid. It's a nice little non-fiction book that tells about how different countries celebrate the holiday.
For multicultural Christmas activities for kids, I recommend the website Kid World Citizen. They have some great resources there.