I came up with a story recently for my planned fanfic anthology series "Flurry Heart's Story" and in it, Discord, Celestia and Luna are featured as children. "But how did this happen?" you might ask. Well think about this: the only characters we've seen use age spells are Trixie with the Alicorn Amulet and Starlight when she turned herself and Sunburst into kids to have them relieve their past (though that one might have just been an illusion). Makes you wonder. Or maybe they're time-traveling versions of the characters from thousands of years ago? Well in my headcanon, Discord is actually a thousand or so years older than Celestia and Celestia would have been an adult when Luna looked like this as it is depicted in my "Age of the Alicorns: Chaos Rising" fanfic so this must be a spell gone wrong. Or is it? All will be revealed, and I am sure you'll like the results.

Btw, some of you probably already know this, but in my headcanon, Discord was born as an alicorn back during a time when they were more common, and his given name was actually "Accord" and he was good until something obviously went wrong. I like to also think that if that isn't the case, Discord started off as a pony and slowly evolved over time to look how he does now as he used his powers. I actually originally wanted him to have the same build as Snails, but I ultimately decided he'd do better as a regular colt. This is what my design for Accord looks like for anyone interested:

https://www.deviantart.com/aleximusprime/art/Accord-puppet-basic-angles-365990183