What is the funniest joke for kids?

Knock knock.

Who's there?

Interrupting cow. Interru...moooooooooo!

The trick is when they are going to say, interrupting cow who, you interrupt them by saying moo!

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My personal favorite joke is:

Why did the mushroom go to the party?

Because he's a fungi!

there a lot more kid's shows that actually have hidden adult jokes. I just google it and I found this link: ww.hahalol.net/2014/10/adult-jokes-in-kids-shows-part-1-dirty-jokes.html