When Did 5 Year Old Humour Get So Morbid?

Younger Son: Mummy, I'm going to tell you a joke.
me: Ok!
Younger Son: Why did the bag cross the road?
me: I don't know, why did the bag cross the road?
Younger Son: Because he didn't think a car was coming. (pause) But a car was coming. And it came around the corner right as he crossed the road.
me: .... ok.

And We Wore Flour Sacks To School, Too.

Older son: Mummy did you know there was a time when the internet wasn't even invented?
me: Yes darling, I was actually alive then.
Older son (utterly amazed): WOW.

Hybrids.

Older Son: I'm being a unipeg!
me: (baffled expression)
Older Son: I'm half unicorn, half pegasus!
Younger Son: I'm a pegacorn!
me: Well alright then.

Alas, I Will Never Be Cool.

Older Son: I will have a band, and I will call it 'Classic'.
Younger Son: I will call my band... 'Bananas in Pajamas'.
me: You know, you could be in a band together. And you could call it 'Classic Bananas'.
Older Son: That's very... interesting, mummy.

Sneaky And Proud.

Older Son: And (kid from school) was being mean to me and the other kids too!
me: Oh dear. And what did you do?
Older Son: I cried and asked them to stop it.
Younger Son: But I told (kid from school) that I was on their team, so they wouldn't be mean to me. I tricked them, didn't I? Hah!

He's Got A Point.

Older Son (screaming angrily): No! Even if I do something to you, doesn't mean you do it back!
Younger Son (after a brief pause for consideration): Well you shouldn't have done it in the first place, then.