"Oh, you are!" Tina reassures as Leah sobs. "Much bigger than you were last year! You're already three! And Mama loves you so much!"
As Tina continues to try to calm Leah's crying, Leah realizes something. She's not the only one who's had something done to their brain. For some reason, Tina thinks Leah is a toddler. And not just any toddler, her biological daughter!
Leah's sobs increase in volume at this realization. How can she be a big girl again if Tina- Mama- whoever this lady is, doesn't know she's supposed to be a big girl? She feels her pullups get warm as she pees. Mama doesn't notice. She just puts a binky in Leah's mouth, then puts her in the seat of the shopping cart.
The binky calms Leah down enough that she can think. If she wants to be a big girl again, she has to figure out why Mama thinks she's not one.