This one is from Ed Carter in Guatemala or somewhere in that part of the world:
A father asked his 10 year old son if he knew about the birds and the bees.
"I don't want to know!" the child said, bursting into tears. "Promise me you won't tell me."
Confused, the father asked what was wrong. "Oh dad," the boy sobbed, "when I was 6, I got the 'there's no Santa speech'. At 7, I got the 'there's no Easter Bunny speech'. When I was 8, you hit me with the 'there's no tooth fairy' speech. If you tell me that grown-ups don't really fuck, I'll have nothing left to live for."