At any craft store they should have a section of plain (thin) wood objects. During the off seasons its anything from frogs & cats, to apples & oranges. During the holidays they usually have bells, reindeer, santa clauses, etc.
It would be fun to get a bunch of those and paint them however they wanted, or you could stick felt to them, pipecleaners, pom-poms, glitter, etc. It would be small and ship well. The adults could punch the hole and string the ribbon through. If you do it, have the kids write a message on the un-decorated side. You could do the same thing with foam sheets, just pre-cut the shapes for them, or have the 11 year olds help cut the shapes.
When I was in girl scouts one Christmas we all made wreaths for our parents. All it was, was a medal ring you buy at craft stores, and pieces of fabric in holiday patterns tied on it. They just cut the fabric into strips and then we tied it on, all the way around the circle, and hung two pine cones by a ribbon from the middle. Ours was the largest ring you could get, but you could easily get smaller ones, and replace the pine cones with jingle bells.
Ok this is the last one I can think of. My mom used to get cinnamon sticks, hot glue three of them together (2 on the bottom side by side, then one on top of those) and tie a Christmas-y ribbon around it, attack a holly leaf and those little read berry looking things (the fake ones) and hang them around the house and on the tree. It made the whole house smell like cinnamon and they don't go bad. You just have to occasionally rub them to waken the cinnamon smell. Might be nice to send them a smell of the holiday.
Have fun!!!