I’ve fed adolescent mice to hatchling royals, and it’s a good fit. Full grown breeding mice, might be a bit too large for a hatchling, but I would never feed any mouse smaller than a small adult/adolescent mouse. Pinkies and fuzzies are just too small. I tend to feed whatever diameter the juvenile ball python belly is, I feed a rodent of the same diameter belly, indeed that big or even little larger, since rodents are furry and appear thicker than they really are sometimes.
It still amazes me how large a prey pythons can kill and swallow whole.
Kaos Balls