The dream Anakin wakes up rest of the events up to Hayden saying "It's just a dream"
Anakin walks over to where his lightsaber is
Anakin: I want him to have this. I want him to become a Jedi.
Padme: Him? Why do you think it's a boy?
Anakin: He was in my dream.
Padme: Now how could that be a bad dream?
Anakin: There was something else ... You die in childbirth. [rest of scene plays out]
I just rewrote one of Padme's lines just now. (Him? Why do you think it's a boy?/Him? How do you know it's a boy?) Anyways, since there's intercutting in the birth of vader scene it's probable that Padme told Obiwan. Even, if you don't include the Vader birth scene it's probable she told Obiwan before the surgery began. That's where Obiwan's line comes from. It also, takes care of Vader knowing about Luke but, not Leia... Though, it would only be accomplishable through reshoots....
