really really depends on..

what they are interested in, if they're girly/nerdy/tomboyish etc. You could make them something, bracelets, anklets etc (find out their favorite color), if they like to read get them a book, again, depending on what kind of material they like to read. Or, you could even bake them something (even more cute bake it into shapes of animals, etc), or get them materials they need and let them make their own gingerbread house.. I don't know there's so many options, but ultimately it depends on what they like. You could even ask them what's on their wish list for xmas.