^ Interesting idea. I had a similar thought once, when Natsu couldn't pass the rune barrier during the Fighting Festival arc.
Of course the DS don't seem to be their literal parent dragons themselves (hence why Igneel and Grandine could meet independently). But it's also clear that they are not just some ordinary human children raised by dragons a few years before the start of the story.
I think, either Hiro might play around with that body/spirit/soul theme... so the DS could hold some "essence" of their dragons in form of their body or their spirit... etc., while whatever else is left is still existent independently of them.
Or (more simple) they are their dragons' real children (and by that dragons themselves) that were turned into or born as humans somehow.
@Buck09: I understood it the way that all anti-human dragons were exterminated by humans. And then, afterwards, they started turning on the friendly dragons, too - eventually (almost) extinguishing them as well.
In other words, my guess is that the "original" anti-human faction won't be featured much in the future. Depending on what will happen with the surviving dragons during this arc, there might be room for some formerly friendly dragons that *now* hate humans and seek for revenge. But this is of course pure speculation