My son (9, 8 last year) was asking questions last year and found one of my flub ups ("Mom, there's a package out there that says DS Case on a postit!" -- Oops:smirk: ), but a story from his sitter told her he still believed...
They were all in the car, and she asked who believed in Santa. Of course, nobody wanted to be the first to raise the hand, so they all kind of looked at each other... Then my son speaks up and says, "Well, my mom can't afford to buy all the things Santa does, so he must exist!" All the other kids agreed and his sitter had to try REALLY hard to not have a heart attack from stifling her laughter!
I guess it does pay to take DS through all the clearance aisles ("Look mom! Clarence!") and let him know realistically when we can't afford something:)