Surrealist knock-knock joke

Peter the Neighbor and his older brother Sam the Neighbor introduced James to knock-knock jokes recently.  (They are three and five, respectively, and are as gods to this two-year-old.)  James, naturally, decided to throw himself into knock-knock jokes, but he doesn't quite have the format down.  He told me this one in the car yesterday:

Knock, knock!

Who's there, babe?

The door!  Hi, door.