Well, I can't speak for Eiken and Ebiten because those are the only two on that list I haven't seen, but for the rest, I wouldn't really consider them shotas because they aren't really distinguished from an average high school male in their shows. The artstyle for Nagasarete Airantou might make the protagonist seem like a shota, but as far as I remember, he's just a normal boy in the show. The protagonists in the other shows look the same age as the rest of their high school peers.
I only saw the first episode of Kanokon a while ago, so I don't remember for sure, but isn't he treated as short in the show?
Well, elementary school boys come to mind when I think of shotas, so maybe my frame of reference is different.