Yeah, I think that most of the jokes offrered here are a little sophisticated for a 4yo.
A few years ago I was hanging out with a 4yo. Now this is a really bright kid. He knew more at that age about the Apollo space program than I ever have. But his sense of humor was still a little undeveloped. We were telling knock knock jokes in the car, and he laughed at all of them, but it was clear he didn’t understand them. The ones he told were along the lines of
Are you doing some sort of routine for kids (at a birthday party or something)? Or are you just trying to come up with jokes for some kids you know? Because what 4 year olds REALLY like is slapstick. Hit yourself in the forehead and fall down. You’ll have them rolling.
For preschoolers there’s not much you can do verbally - there’s almost always some visual element involved. Having said that, contradictions work very well. “I was taking my goldfish out for a walk” would be met with giggles and shouts of “No - a dog”. Or as C3 said, slapstick. Putting your glasses on upside down, tying your shoes together, etc. Little kids LOVE it when you do something the wrong way and they’re suddenly the experts.
The interrupting cow and the orange/banana knock knock joke are the favorites among my kids, and they’ve been telling them for years (since they were about 4). Comments upthread are right though- if the joke is “funny” because of a play on words or double meaning, most 5-year olds won’t actually find it funny, but will laugh because it’s a joke.
For a long time my 6-year old’s favorite knock knock joke was one she made up:
Knock knock
Who’s there?
Pizza
Pizza who?
Pizza pie!! [then she and her sister would giggle until they fell over].
This is one of my personal favorite knock-knock jokes. I tried a couple of them (including this one) on my four-year-old a couple of weeks ago, and now my wife and I are occasionally treated to this fine example of the comic art:
“Knock knock!”
“Who’s there?”
“An interrupting cow has come!”
“An interrupting cow who?” — My attempt to salvage what’s left of the joke.
“Don’t cry, it’s only a joke!”
I find this as hilarious as my preschooler does, but for a totally different reason. The moral of the story: Yeah, four is a little young for real humor.
What goes clomp clomp clompsquishclomp clomp clompsquish?
An elephant with a wet sneaker.
Another good one is to say “I’ve got a knock-knock joke. You start.”
Kid says “Knock knock.”
You say “Who’s there?”
Of course then the kid has no idea what to say after that…
That joke is in a joke book that’s in the Dr. Seuss collection (but isn’t by Dr. Seuss - you know the ones I mean?). I had it when I was a kid and my older son got it out of his school library a few months ago, which was really cool. I hadn’t seen it since I was about 6.
Another joke from that book:
What did the big firecracker say to the little firecracker?
My Pop’s bigger than your Pop!
Of course, when my brother told it at the dinner table, he said, “My crack’s bigger than your crack!” which my parents found HILARIOUS and still talk about nearly forty years later, poor guy.