Funny Dirty Joke

A son is in his room and the mom comes in and says do you need to shower and he said yeah I need to shower and the Mom says you can shower with me if you don't look up or down as soon as the get in the shower the son looks up and asks the Mom what are those and the Mom answer and says those are headlights then he looks down and asked what's that she says it's the tunnel the next day the dad asked the son do you need to shower the son said yes and the dad said you can shower with me as long as you don't look down as soon as they get in the shower the son looks down and says what's that and the dad says that's a train that night he has a nightmare and asked his head parents if he could sleep with them and the say as long as you don't look under the covers once he gets in the bed the son looks under the covers and says "MOM TURN ON THE HEADLIGHTS THE TRAINS GOING IN THE TUNNEL"