Celestia is feeling maternally nostalgic, Twilight accidentally turns her body into that of a filly, and Luna experiences the joy of being an aunt. Also; Trixie will eventually become a guard for a day, Discord will at some point have a few good laughs, and Spike will have to deal with his big sister suddenly being shorter than him when he's actually informed.
This is a Twilight/Celestia mother-figure/daughter-figure family fluff filled story stuck together with humor. Pretend this thing has a fluff tag. Also, there will most likely be no pairings in this story that aren't canon-compliant.
Note: Updates shall be erratic. Very erratic. I apologize in advance.