Her 9-year old grandson came in from outside and asked,

“Grandma, what’s that called when two people sleep in the same bedroom and one is on top of the other?”
Taken aback, she decided to be honest, “It’s called sexual intercourse.”
“Oh, okay,” and he went back to play with his friends. A few minutes later he returned saying angrily, “Grandma, it isn’t called sexual intercourse. It’s called Bunk Beds and Jimmy’s Mom wants to talk to you.”