Responses
It's called infantile regression, common troupe where the adult mind slowly degrade to a child to match their body
It's not that common to be honest. Most stories about regression have the adult mind in kids body but this type of stories where the regressed person is being a kid without even trying is too rare to encounter.
I just love how the MC can be a kid again despite hime being an adult in the inside. He can enjoy his moment as a kid again without any problem. No blusing moments with other kids instead he see them as an equal kids or siblings