Who's on First

Morgan and Sebastian, both age 5, in the car:

S: I can do a joke, wanna hear?
M: Okay.
S: Knock, knock!
M: ____________...
S: You say, who's there?
M: _____...
S: Knock, knock!
L: Who's there?
S: Ummm, hot dog! Get it, a DOG, is HOT! He's cooking his self!!

S: Knock, knock!
M: Who's there?
S: Know why? Cow pie! A cow that's in a pie!

S: Why did the skeleton, why could he NOT cross the street?
M: Because he was just bones?
S: He didn't have any guts. Get it? He didn't have any mush because he was just a skeleton.
M: Are you joking? [to me] I'm asking because he sometimes does jokes.