Daring Do was pushed her into a Fountain of Youth and was regressed into a foal. She then finds Ahuizotl (who was also regressed into a kitten). The two have to trek through the jungles of the Tenochtitlan Basin and find a way to turn back to adults
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.
(An indirect sequel to "Finding Shining" and "Finding Sunburst" by Foal Star.) Princess Cadence willingly turns herself into a foal to spend time with her daughter. But Cadence soon desires to have her own foalish adventure and slips away.
(Story idea requested by superfun. Contains age regression, diapers, and diaper useage! Reader discretion is advised.) When Diamond Tiara and Silver Spoon lose a bet to the CMC, they are turned into foals for a week. The CMC must care for them.
Celestia has reached the eldest age for an alicorn, and in order to continue ruling Equestria, she must once again transform herself back into a filly.
Discord wants a family, but since he's too embarrassed to ask he decides instead to use the mane six as his foals. Regression and foalish antics ensue.
Luna wants to go trick or Treating but Celestia is emberassed and decides its about time they stopped. Frustrated Luna turns Celestia into a foal and now has to care for her during the festivites.
(Rated Teen to be safe.) Cheerilee decides to turn herself into a foal, so her students will have hoofs on experience taking care of one. But are her students up to the task of caring for their foalified teacher?
Hoity Toity is suddenly turned into a foal, and his collection of foal clothes went missing. Now he'll have to go to Manehatten and win a foal fashion show with the help of Rarity.
Spoiled Rich is turned into a foal by a strange nanny with myseterious motives. Diamond Tiara finds her mom, and has to care for the mare in her new foalish state.