Cute story :)
Btw: I wondered about this for a while... but most of the time when Koutarou is shown he seems like a little bit of an idiot compared to the rest of his family. I know he's the youngest, but still...
I have a theory as to why Cotaro seems dumb compared to the rest of the family.
If you notice how little he shows emotion, his incomplete speaking, his flat tone, and his lack of imaginative play, but also the signs of his creativity being good (making mu's snowmen) and his drawling speech, those are... actual signs of developmental problems. More specifically, special needs. I think out of all of the special needs he could have, it is likely he has some form of Autism. That would explain his lack of basic human skills that even a 4 year old would have.
