Go over to the mad potter's blog and add it to the list. Must be suitable for kids.
Speaking of jokes....
A woman gave her husband a sealed box and told him not to open it until she was dead. The husband put the box in his wardrobe for safe keeping but couldn't stop thinking about it and what it might contain.
He kept taking the box out of the wardrobe and staring at it. Many times he started to open it but remembered his wife's instructions and put it back.
Finally, after weeks of this he weakened and decided to open the box.
Inside were half a dozen eggs and a hundred thousand dollars.
He put the box away again but, again, it preyed on his mind.
After another couple of weeks he decided to speak to his wife about it.
He told her that he couldn't stand it any longer and had opened the box. "Why are there half a dozen eggs in the box?"
She answered, "Each egg represents a time I was unfaithful to you."
"And what about the hundred thousand dollars?" he asked.
"Every time I got to a dozen eggs I sold them."