My son was once bothered that girls got to give birth to babies but boys didn't get "anything special." I pulled him away from his gloating sister and said,
"Listen, you'll learn more about this when you're older, but your penis does an important thing. The Dad helps make babies."
"Oh! How?"
"I'll tell you more when you're older."
He thought deeply for a second.
"So before I have kids I need to learn how to use my penis to get the baby out..."
"Uhh, no. You need to help put the baby in."