I'll update this as soon as I have the time to actually write it!! 
(RIP me living in the center of virus outbreak)

But short answer, timing is basically that - generic fantasy timeline LOL

Lots of civilization! The village I pictured is moderately isolated and in the mountains with a large river. There are other villages but they aren't really that close and I would say that the general education of people in the area is low because they are so isolated. But not so isolated that there wasn't a violent murder....and a sexual encounter was that consensual or not (haven't decided).

The water child is something that isn't common knowledge outside of that village. If it weren't obvious, there are three others will similar titles but for the other elements. At this point, the lore isn't known to my narrator (who will be Maya for now in the time jump) but there is someone that knows it in more detail - someone that shouldn't (the mom, hint hint). In the village that I started in, they don't know about the others but I am going with those that are connected to fire MIGHT know more - at least someone does. Maybe it is a little less isolated, maybe the information has been lost to the water child'S village population. Idk yet. 

I would say the lore of each place that has a person like this though is probably a bit different, though the origin is obviously the same. Like, maybe they aren't "fire child" "wind child", etc. They could be called by something else but I would think they would be cherished in the same impersonal way. It's definitely in the blood of the people in their respective area though.

Excuse my word vomit. Apparently I had more to say than I though LOL