give it to me straight, mom

sitting in car, waiting for green light:

e (almost 4): we are going on an airplane today.
me (much older): yes we are.
e: what makes the plane go up?
me: the wings do that (trying to not get too technical).
e: but, how?
me: the wind blows on the wings and that makes the airplane go up in the air (there, i think thats about the reach of ur understanding)
e: but, why?
me: the wind does it, e.
e: but why does the wind do that?! (getting frustrated).
me: (ok....u asked for it kid) the wing of the airplane is made a little bigger on the top, so when the plane goes really fast, the air has to pass over a larger area. the difference in distance makes the air have to go faster on the top of the wing, this creates a difference in air pressure. the lower air pressure on the top of the wing, sucks the airplane up in the air.
e: ooooohhh.....i gotcha.

for all the rest of us, i recommend howstuffworks.com.