Classic! I wish I could remember the dad's answer to Calvin's question about where the sun goes at night.
How's this???
C:"Why does the sun set?"
D:"It's because hot air rises. The sun's hot in the middle of the day, so it rises high in the sky."
D:"In the evening then, it cools down and sets."
C:"Why does it go from east to west?"
D:"Solar wind."
M:"
DEAR!"
Not the one I was thinking of, but very funny. :o)