Clones in the Mario World
A little fact many people overlook is the cloning of characters in the Mario World through various means.
One way is through power-ups such as the Copy Flower from Mario & Luigi: Partner's In Time, and the Double Cherry from Super Mario 3D World.
Another way we've seen was through Belome is able to make clones of Mario and friends.
Another way is magic like we see with the Fake Bowsers who are enemies like Goombas transformed by magic. As well as illusion copies we see characters like the Koopalings create with their magic wands.
Characters like the Yoshies, Mario, Luigi, and Wario are also able to put on special hats that allow them to transform into one another, thus technically making clones. However, these hats don't work on everyone as seen with the Goombas.
Since clones are so common this could explain that second Mario seen in Donkey Kong Junior, or that could just be Luigi.
But this could also explain all the Luigis in ScareScraper and ScreamPark, these Luigis could be clones created by any of the various means listed above.
We have also seen Bowser make bubble clones of the main cast before as well.
Finally is the Mini Bowsers, so something interesting we've seen them do is duplicate themselves in Mario Party 5, which would explain why there is so many of them. But there is an extra detail here.
When working on this post I found something, the phrase Kuppa-sama no bunshin being used to refer to Koopa Kid. The word bunshin while it can mean offspring and the localizers seem to have interpreted it to have mean that it doesn't just mean offspring. The word bunshin can mean alter ego but primarily clone or doppleganger.
The word bunshin I've seen used for specific type of Ninjutsu called bunshin no jutsu which means exactly that.
So the Koopas Kids are Kuppa-sama no bunshin or Bowser's clones/dopplegangers. The cloning thing also seems to be a theme with the Mini Koopas due as seen in Mario Party 5.
Written by Eris the Lorekeeper