It’s not my favorite kid joke but it’s a solid #2.

So the 3 year old grand-daughter asked her gramps, "Where does poo come from?"
Caught off guard but being a grandfather and knowing he’s expected to know just about everything, he said, “Well, you just had breakfast, right?”
"Yes sir”, she replied.
"Well, the food goes in your mouth and down into your tummy. Our body takes all the good stuff that it needs out of the food and then what's left goes down to your bottom and when you go to the toilet, what’s left over comes out as poo."
She looked very confused and stared at him in stunned silence for a few moments.
Then, with a child’s nervous voice, she asked “So where does Tigger come from?’