Are these parent motivated by their own desire for a child of the opposite sex? Obviously the request didn't originate from the kids themselves, or if they did, shouldn't be entertained...
I knew someone years ago who everyone made fun of as a he/she... First time we met, this person was a she, and years later when we met again (bought drugs from them) she was now a he. Apparently he was born a hermaphrodite, had both organs... Someone, not sure who, either the doctors or the parents, decided they should be a girl, so she was raised a girl... When she got old enough, she switched to living as a guy, which was much better, apparently his upbringing really scarred him, he was really messed up...