Dawn is at the age Buffy was when she was Called, so does it even make sense to think of her as a child? Of course, the ability to relate to adults as peers is relevant for teenagers as well.

What strikes me particularly about your mention of Dawn/Giles is that that gets my brain going along the lines of non-adults who want to be (treated like) adults, which is where my interest lies (having been one of those children/teens), whereas thinking about Ari's talk about the Matilda movie (which I haven't seen) I find myself thinking that Matilda found a person with whom she could safely be a child (Ari's description of the ending montage sticks with me particularly) and I secondarily think of the idea that Matilda is an adult figure for Miss Honey, which makes sense to me (esp. given Ari's talk about the movie playing up Matilda's Gryffindor-ness) and is interesting also because I'm not sure I see Miss Honey as being able to be on Matilda's level intellectually. (I know at the end of the book we have Matilda finally finding sufficiently challenging material into which to channel her energies, and it's been years since I read the book so I can't remember what grade level she ends up at, but I don't recall ever seeing Miss Honey depicted as particularly intellectual; she's teaching kindergartners, and the big appeal she has is her kindness -- which of course is nothing to sneeze at, esp. given the environment of the Wormwoods and the Trunchbull, but Matilda isn't drawn to her because she is an intellectual equal.)