I stumbled upon a sweet idea while scrolling through tumblr and wanted to share it. Perhaps someone on here has already seen it on there as well. The one who came up wit this concept is known as mud-castle on that website.
Here is the basic premise described by them:
Essentially what happens is the clans are fighting about something stupid again and Starclan is like "You wanna act like kits at a time like this? Fine." And turns the four leaders into 3-4 moon old kits at a gathering. Until the clans can figure out a way to work out their differences for real this time, the leaders will stay like that. Adorable shenanigans ensue. I think it takes place somewhere around the beginning/middle of
Omen of the Stars (they later specify it taking place during
Fading Echoes since that is where Mistystar had already become leader and Russetfur was still alive as deputy).
Here is a full art piece for the AU (also by the creator mud-castle):
Characters in the first panel: Brambleclaw, Reedwhisker, Russetfur and Ashfoot
Characters in the second panel: Onestar/kit, Blackstar/kit, Mistystar/kit and Rusty/Firestar/kit (the latter got confirmed by mud-castle to have reverted back to his early kithood/days as a kittypet and unfortunately thus does not remember anyone from the Clans anymore since he had not grown up with them at that time or even met them yet)
There is also this adorable comic of the kit leaders running away and their deputies having to go find them:
Some more information as well as cute art about that specific AU can be found in this tumblr search or via the "little leaders au" tag on it:
www.tumblr.com/tagged/little%20leaders%20au?sort=top