Ty has always liked wearing and seeing girls in diapers. So he (rather she) wished that every female in the world doesn't develop bladder or bowel control, so they need diapers. It's normal that they wear them without anything else and that they change them in public. Only Ty knows that it wasn't like that.
When the changes were applied, she sees her whole class, and her, wearing nothing but a diaper. She felt the urge to pee, but just for a second, as she was already peeing herself. She decided not to change her diaper by now.
She wanted to make it more interesting, so he wished that this would be like a kindergarten class. All her classmates think they're 4 years old, but it doesn't affect their body. Also, everyone sees them like 4 years old too. When she finished her wish, the room changed to that of a kindergarten.
One of her classmates started crying and yelling "change my diaper". Ty decided to do the same, as she was wet. Soon, her teachers changed both in the middle of the class. Ty thought that it was gonna be a fun day.