There are knock knock jokes for almost every occasion in life. Consider these:
Lettuce in it's raining out here.
Figs your doorbell it's broken.
And why do we bother blogging them? Simple really. Early years are the time when children learn the most and the fastest about language. They learn about the meanings and sounds of words and how these words help them make sense of the world. One effective and fun way you can share with them in this making sense is with the puns and wordplay you find in jokes, like knock knock jokes.