Funny Dirty Joke

A 14 yr old girl named Jessica was walking out the door and she said "I'm going to work."
Her Mum said "She never told us where she works."
Jessica's little brother, Oscar, said "I know where Jess works, but first Mum you said you were a prostitute, What's that?"
The father replies "It's a job where strangers pay to have sex with your Mom."
"That's funny," the boy said, "That's what Jessica does."