Are knock-knock jokes funny?

Two men are having a debate on the comedic value of knock-knock jokes. One is 34 years old, and has taken the stance that knock-knock jokes are not funny. One is 3 years old, and has taken the stance that they are.

In his arsenal, the younger debater, who loves owls, knows the following knock-knock joke:

Knock-knock.

Who's there?

Who.

Who who?

Is there an owl in here?

However, he keeps it to himself until, as the argument hurtles toward its conclusion, the younger of the two produces his trump card. He draws his opponent into the following exchange:

Knock-knock.

Who's there?

Who.

Who who?

[smugly] That's right.

The older man falls to pieces with laughter. He has been championed. The younger man returns to his crayons.