sorry if this is a dumb question in advance, the supernatural species live aside humans right, so that means humans know of realm children and all of the others? the police too? so are crimes investigated knowing that? humans know of vampires and dragons in the sky too?
First off nonnie there's no such thing as a dumb question at all!
So for starters it really does depend on the species. Since Agdoeg has been a Supernatural hub for awhile their city leaders and departments have documents on every species that have ever graced their soil. But sometimes there's a first for everything or that species is just a name/category and not much more.
For example: Blue is the only known Planetary Elf in the area. So most of their information they have is based off of this one individual.
Humans know of these species, but just like race and ethnicity you don't truly know unless you ask or they have outward features to show that they aren't of the human world.
So specifically, using your question as an example, Realm Children, are perceived as humans other than maybe powers and eye color. And to some they are just a legend, or apart of another religions folklore. Meaning that as far as anyone is concerned Nanami Kakuzo, is just a Japanese citizen who moved to Korea.
There are no dragons in the sky on a general basis but if a dragon-blood wants to transform and take flight any humans in the area would definitely see them. For crime investigation, when it comes to reports you would give the species as if you would give the ethnicity of a suspect as well if you're able to tell, and just like a good CSI they would be able to tell in an investigation if a crime was committed by a known species, based off of the damage made, bite marks, feathers/scales left etc. left at the scene.
Of course living in Agdoeg you can infer that most of its inhabitants aren’t human, but with some species you may have to do a bit of digging, some you know right off the bat like incubus Other’s aren’t even on government/police radar.