I want to find a little joke suitable for first-grade children.

One day, I saw an old man squatting in front of the hospital. I went over and asked, "Grandpa, what's wrong with you? Do you have no money to see a doctor? " The old man gave me a look, sighed and said, "Hey, my grandson has a bad stomach. The doctor asked me to test his stool. I packed his poop in a box and used a newspaper. " I looked at him. What's so sad about this? But what he said next surprised me. "Who knows, I was stolen when I took the bus." .....