the simple fact that two people in love have to worry about how people will react to them, that they have to 'monitor their behavior' in some way to avoid giving offense - there is something deeply and fundementally wrong about that.

I agree wholeheartedly. I will, however, add one small caveat. The child in question is so young, that even if his parents are pro-gay rights, he may never have seen two women behaving in such a fashion. More of a "I didn't know that was possible" than a "I don't think that's right." But that probably accounts for the "vaguely" part.