Knock Three Times

People will tell you that kids go through stages. They will rattle off terms like "terrible twos" and "separation anxiety" and describe what the typical baby, toddler, and preschooler is like.
You will dutifully memorize these stages and watch for signs that your child has entered one.
Because of your vigilance in watching for the early signs of the oral fixation or bed wetting stage you might miss the sings of when your child enters the knock, knock joke stage. You might even think, because you haven't read about the knock, knock joke stage, that your child is unique in his or her sudden interest in knock knock jokes. You might be proud of this and say to friends, "Little Johnny is so into knock, knock jokes. It's the cutest thing." Parents of younger children will nod in agreement thinking that knock, knock jokes are a huge step beyond drool-on-your-fist stage which is where their kid is at. Parents of older children will just shudder and possibly convulse at the memory of when their own kids entered the dreaded knock, knock joke stage, which, in a twist of nature akin to the irony of 13-year-old girls being able to get pregnant, happens well over a year before children can actually read at which point they could tell a decent knock, knock joke. Also, despite loving the idea of the knock knock joke, preschoolers don't really understand the knock knock joke.
What's to understand you ask? Only that the knock, knock joke is supposed to be funny and when your four year old tells you a knock, knock joke it's funny that he's trying to tell you a knock, knock joke - but the joke he's telling isn't funny. Because he's making it up, and he doesn't get it, and he's bad at it. And so you end up with:
Him: Knock, knock
You: Who's there?
Him: Bird
You: Bird who?
Him: That one.
And because you are a good parent you will say, "good one!" thereby reaffirming in his mind his ability to tell bad knock, knock jokes. Which will lead to him telling more knock, knock jokes, probably when you are in the car and therefore unable to escape their relentless non-funniness. In this type of situation it's best, despite your Buddhist pledge to live in the moment, to zone the little bugger out. Think of the Queen. Think of what's for dinner tomorrow. Think of what the hell Peter Jackson was thinking when he decided to split The Hobbit into thirds. That man should be bound and gaged and made to sit in the car with a knock, knock joke-telling preschooler. Fifty Shades of Bilbo Baggins.
H even went through a stage when he told bad chicken jokes.
For example:
H: Why did the chicken cross the road?
Me: I don't know. Why?
H: Because the farmer was chasing him with a gun.
Ouch.
The knock, knock joke phase usually takes place around ages 4 to 5. It's followed by the create-your-own soup stage (be sure to have carrots and bullion cubes on hand) from ages 6 to 7, and the bathroom-talk stage which starts around age 6 - and - if you have sons - lasts until they turn 30.

song: Knock Three Times • artist: Tony Orlando and Dawn