Celestia: “Woona, Woona! Come quick!”

Luna: “What is that?” Steps into the bathroom stall

Celestia: “I big filly, watch me potty?”

Luna: “Sure, you want momma to help you-”

Celestia: “No! I do by myself!” Sits on the potty

Luna: “Hehe, are you sure about that?”

Celestia: Fills the seat of her diaper with a warm mush

Luna: Giggles, giving her her bewildered sister a motherly smile “Looks likes some pony needs a diaper change. Don’t worry, we’ll get you out of that dirty diaper and into a fresh new one!”

Celestia: “B-But I p-p-pottied…”

Luna: “Yes you did!” Sticks a pacifier in Celestia’s mouth and smiles