A kindergarten kid probably wouldn't say "pressure" over "i don't know" but the whole statistics with the harvard graduates and the kids is probably made up. Statistics are made up really easily. I think the answers snow, time, air, nature, God.. are all stupid because you can't justify them for everything in the riddle. People just look at a couple parts of the riddle, and if you can make a relation between a couple things they think that that's the answer. Well why would squeezing God make him pop? Why would snow turn pancakes brown?
I think whoever said pressure is the closest to being right. You can justify all the things with different kinds of pressure. The answer "i don't know" is like a lazy way out.