There's another post on here somewhere about the santa issue and kids. I just commented on that the other day. I'll give you a very shortened version of what I said there.
My 5 yo has never believed in Santa. We have told her to keep quiet about it. She is still a child, she often ignores what we say or forgets, and tells most anybody who talks about Santa, be they adult or child, that Santa is not real. If she sees a Santa picture in the store, she blurts out, "Santa's not real he's fake!" She's not doing it to be mean, she's just a kid and she forgets. You have no idea really if that kid's parents told them to keep quiet about it, it's quite possible they have talked to her numerous times about it. The fact is, they're a kid and often have little or no sensor over what they say. That takes time to develop, and even teenagers still don't have that sensor sometimes, so it's not really fair to be angry about it at the kid or parents. Put yourself in the other paren'ts shoes and pretend your kid is the one out there telling ppl's kids santa doesn't exist... what are you going to do? Ground her? Take toys away? Keep her isolated and away from other kids so she doesn't spoil the santa thing for other kids? All becuase she's telling the truth?
My rant is over now :)