Then, Jon got an idea. And it wasn't one of those ideas that people randomly get. No, it was an idea that he got because he was looking at and smelling those old sandwiches. They had been covered in mold and smelly and the only thing which kept it from being even worse is that the sandwiches had dried out long before the ten years was up.
Jon recalled that in history, sometimes people could eat moldy bread and hallucinate or go crazy for a while, if it was the wrong kind of mold.
"I wish that Karyn and my Mom think and act like they're ten years old because they ate some moldy sandwiches that made them think they're ten years old."
Once they recovered from the mold, they'd still have ten year old bodies. But the wish that gave them ten year old bodies was made where they could hear it, so everyone else would think they're ten years old, but they would have their own minds.
"I wish that Karyn and my Mom would go to bed now until they're well."
The stone was smart enough to know who 'Mom' meant even though she wasn't a mom at the moment, and the two went off into the bedroom, giggling like ten year old girls.
It was dinner time when they had finally recovered from the mold and acted their own age again. Karyn, accompanied by Jane (Jon's mother), her best friend, opened Jon's door and yelled, "Jon, have you figured out how to change us back?"
"Karyn," said Jon, "I think you've forgotten. I changed you two on purpose. Everyone else still thinks you're ten year old girls. You did it to me, it's far for me to do it to you."