Jon picked up Karyn/Barbie and said "I wish ... I had a bunch of these Barbies." Jon was going to wish for something else, but right when he was making his wish, his mind became that of a 10-year old girl.
The stone glowed and the hall was filled with at least a dozen Barbies that looked exactly like the Karyn/Barbie.
Now, since both Jon and his mother were 10-year old girls, there had to be a parent or guardian that took care of them. And that person was just coming in through the front door at that very moment.
It was ...