Normally for isekai, reincarnation, transformed into new body etc type series I treat the characters as they physically are(unless it is temporary, like magical girl or whatever). Someone reincarnated, they have a chance to be a kid again. Etc.
And for most of the time there are not any issues with that.
This series is one of the few that forces me to do the opposite. But damn are these oji-sans creepy as hell, whether original or new bodies. It almost gives me 4th-hand goosebumps.