I think it's a little hommophobic well, what I mean with that? Hm they are her parents, so normally it's normal for the child to think they are lover, it's not a straight world, the child live with that since her born, so the real question she can have is, can a male and a female be lover too? The child grow up and learn that's normal in the 2 way I think the creator didn't think about it and normally when you create a manga you have to have a good logic