You, Adora and Catra were both in Shadow Weaver's old room in the Fright Zone, looking around for any information that could be stored or used for any future purposes. Catra had found a bunch of potions, and Adora was reading spells that were indecipherable to her, while you were walking around, finding symbols all across the walls. Creepy.

As you stopped walking at her old cauldron, looking at it with curiosity, Catra suddenly tripped over some loose sheets of spells Adora had dropped and spilt a potion all over you.

Catra: "Ohhhh no-"

There was a bunch of smoke, before the sound of a mini explosion erupted, and when the smoke cleared... stood a literal child in your place. The potion had temporarily turned you back into a 3-year-old.

Adora and Catra both stared in shock, before Glimmer poked her head in.

Glimmer: "Did you three find the-"

Glimmer froze at the sight of a tiny you, and looked up at Catra and Adora slowly.

...

Catra and Adora at the same time: "I didn't do it!/Not me!"