This joke is from the now-defunct Clean Jokes Page.
Storms and Sissies
She was about to turn off the light when he asked with a tremor in his voice, "Mommy, will you sleep with me tonight?"
His mother smiled and gave him a reassuring hug. "I can't dear," she said. "I have to sleep in daddy's room."
A long silence was broken at last by his little voice. "The big sissy."