Why the sourpuss reactions? I think it's a brilliant advertising stunt which accomplishes exactly what it aims for: catching would-be buyers off guard in a humoristic way. It's a hyperbole and I happen to think it works well, brought a smile to my face even though I do not belong to the target audience.
Why is it so hard to admit that this IS a cool advertising stunt, well thought-out and executed to perfection. The kids were trained and prepared, the customer's surprise caught on video. What's there not to like?
PS: It wouldn't make me buy anything with windows in it but then I'm a hardcore PCLOS longtimer so I'm really corrupted. I know what the word "simple" actually means 
As advertising goes, it
is a good campaign,
except, I'm getting mixed messages (disclaimer: I'm critical of almost all advertising, and tend to focus on their faults):
1) Is the point to tell us the kid is smarter than us (adults)?
2) Is the point that kids are not smart, but this OS is so easy, they can "get it"?
3) Is the point to highlight the fact that this is such a divergent approach, that a person without preconceptions is required to grasp it?
4) ...
I'm sure there are others, if I gave it any serious thought...these just came of the top of my head
(PS, it is hyperbole, as well)
