Other than the drawing skill here, it's interesting why a kid thinks about demons attacking god. And why demons look like that for him.
At this point in his life, Michaelangelo was probably apprenticed to Ghirlandaio. This wasn't a freeform doodle, but likely something of a homework assignment. It was common for young artists to be given famous works to copy, or common religious scenes to remake.
It looks like the figure they're attacking is meant to be St Anthony, rather than God.
As the article says, it's based on Schongauer's The Temptation of St. Anthony. There's even a version by Salvador Dali.
It's just a reflection of his education. Even today, many children are raised with religious education that includes stories of demons attacking people. Kids love scary stuff; monsters, battle, etc.
It makes me wonder what his home environment was like where he could put such detail into a painting. Something like that isn't made in an afternoon or weekend; and it definitely requires parents to provide resources and moral support.
Demons look like that in Medieval and Renaissance paintings. "Red dude with horns" didn't become the standard depiction of demons until much later.
12 years old is pretty old for a kid. I remember trying to reason through my grandparents’ religious beliefs at or before age 9, and they had taught me about lots of different demons, gods, etc.
It isn't an original work, but actually a painted version of a famous engraving by Martin Schongauer.
https://en.wikipedia.org/wiki/The_Temptation_of_St_Anthony_(...