Rainbow Dash finds 2 matching necklaces that she thinks will look perfect on Rarity and Applejack. But turns out, those necklaces make their wearers turn into foals.
Mistakes can occur even when you're too advanced for your studies... Twilight learns just that when a magical mishap results in both of her pegasi friends becoming foals.
Rainbow Dash and some of the other recruits from the Wonderbolt Academy were regressed into toddlers. Now they have to relearn how to fly to escape the Daycare and find Twilight.
Starlight Glimmer's plan to go back in time had backfired, and she turned herself into a foal and went back further than she intended. Now she has to find a way to return to her own time and into her adult body.
(A collab with Latecomer, open to all authors. Stories should be SFW with some potential PG content, rated Teen to be safe.) A collection of stories involving various characters undergoing potty training, to varying results.