MCA
MCA, as painless_j terms it, is "magically changed age".  Another identifier for these fics is "de-aged", but I'd like to add the prospect of aging to both of those definitions as well.

It irritates me that I can't find an MCA list out there.  Perhaps I'm not using the right search terms.  I've seen baby lists, but that's not only what I'm going for (and there are lots of poorly written baby fics).  I'm just as willing to see something like "Big" or "Freaky Friday". 

Feel free to help me add to my list.

Babysitter, by Spye.  H/D.  "The Curses cast on Draco at the end of fifth year are removed incorrectly, leaving him in a state requiring that he be taken care of.  Who better than Harry Potter?"

Charles Alexander Tompkins by Taran.  Attempted murder, hexes gone wrong and an old man bring Severus Snape back to Hogwarts as a different man -a 16 year old man.  HP/SS, 15 chapters, Complete.

Child of Mine by Lina Inverse the Dramata.  Harry's turned into a baby and the Potions Master is stuck having to take care of him, but now things are different. 17 chapters as of May '06

The Curse of Fate by Mistress Nika.  Immortal Harry, after watching friends and family die over thousands of years, only wants to join his loved ones in death. Believing he's found a way, he sends himself back into the body of his infant self, vowing to change his fate.  23 chapters as of January '08. 

Death Eater Takes a Holiday  Dumbledore decides the staff deserves a break without having to worry about things for a while.  And while he's at it, he might as well remind them what their students are going through.  A few more teenagers get added to the list staying for winter break.  85 chapters, WIP

Decreso Aetas, by Harry's Gryffindor Angel. Summary: "An accident occurs in Charms class that leaves Draco looking after a...slightly different Harry...How will they live through it, and how do others take the change?"  HP/DM; WIP

Fire and the Rose:  Hermione and Snape switch bodies.  It was an accident, but will Voldie understand?  reminiscent of "Freaky Friday."  I'm not entirely sure switching bodies works, but technically a student must act an adult, and an adult a student.  HG/SS 40 chapters, complete.

Harry Potter and the Ferratilis Potion: At the Dursleys the summer after Sirius' death, Voldemort sends werewolves to attack Harry. Taken to Grimmauld Place by his rescuer, Severus Snape, Harry devises a disastrous plan to rescue Sirius from the veil, resulting in his being transfigured into a baby. Snape is the only one who can brew the potion to restore him, and is the only one to realize that Harry still retains his 16 year-old-mind. Over the summer and the first two potions which restore him to age eleven, Harry begins to feel that Snape is the only one who understands and can protect him. Is he right or has his deaging muddled his thinking? WIP, 25 chapters as of Aug '07

An Innocent Gift, by Amber Dream. WIP. Author's summary: "Due to Voldemort's... insanity, Severus is forced to take an unidentified potion. When the effects of said potion take place, what does Dumbledore do? Send him to the one person he feels he can trust of course. Not slash." Snape is turned into a baby. 7 chapters as of June '07.

The Living Years by DementorDella:  "Severus Snape makes the ultimate sacrifice for Harry Potter. No, not that sacrifice! The other one! And finds Sanctuary in the most unexpected of places."  35,000 words, complete.