If you have children, sometimes what comes out of their mouth shocks you.  They are not burdened with a need to conform to expected social behaviors, and they just speak their honest thoughts.  There have been many times where I should have kept a straight face when my son spoke, but all I could do is roll around laughing . That is why I find little johnny jokes so funny.

If you are to look up the definition of a little johnny joke on wikipedia, you would find the following definition:

"Little Johnny jokes are about a small boy who likes to ask embarrassing questions and has a very straightforward thinking."

The following is a clean example of a little johnny joke from Funny Jokes:

A professor of chemistry wanted to teach his 5th grade class a lesson about the evils of liquor, so he produced an experiment that involved a glass of water, a glass of whiskey, and two worms. “Now, class. Observe closely the worms”, said the professor first putting a worm into the water. The worm in the water writhed about, happy as a worm in water could be. The second worm, he put into the whiskey. It writhed painfully, and it quickly sank to the bottom, dead as a doornail. “Now, what lesson can we derive from this experiment?” the professor asked.

Little Johnny raised his hand and wisely responded, “Drink whiskey and you won’t get worms!”