DS9 still believes, but it could be due to Santa and the Tooth Fairy being pretty persistent.
Yeah, those guys (and the Easter Bunny) can be that way, can't they?
DS6 is still a believer, but my family tradition is rather active and aggressive when it comes to holiday characters. I had to insist on being off work for Christmas year before last, because we had a meltdown over having to move Easter to Wednesday when I was off. His friends told him the Easter Bunny would not come on Wednesday, and I had to explain that I have known the Easter Bunny all my life and he would come when I asked him to! Sure enough, he did, and DS was proud to tell his friends about that one. But I knew I couldn't get away with it anymore, so I had to be off for Christmas.
I had to laugh a couple weeks ago--DS wanted to take his new calculator to bed, and was trying to figure out where to put it so it wouldn't fall out of bed. I told him to put it under his pillow. He said, "No, I can't do that, because then the Calculator Fairy would come and take it!" I had to admit that I have never seen the Calculator Fairy--I guess that's because I never put a calculator under my pillow!