Now that is exactly the type of Knock Knock joke my mum comes out with. To our frequent hilarity she just doesn't understand how they work.
My personal favourite is:
Mother : Knock Knock
Us : Who's there?
Mother : Tomato
Us : Tomato who?
Mother (brightly) : Tomato sauce. There - was that funny?
Us (rolling on floor) : No, it wasn't.

And then of course there is always: Mother : Knock Knock, who's there? Oops! That's not it, is it?


Kris