There is a definition somewhere here of a natural born citizen that requires both parents to be US citizens.
That is a definition, but it is probably not the correct definition. Until Barack Obama ran for President, every definition of US citizen I ever ran across only mentioned two catagories:
Natural born citizens, who got their citizenship at birth
Naturalized citizens who got it after they were born.
The both parents must be US citizens definition appears to come from a French legal text and is, to me, not relavent.
I’m a strict constructionist. The plain meaning of “natural born” means having that condition at birth. If someone is described as a natural born athlete, it means they were born that way. It does not mean that both of their parents were athletes and that they were born in a stadium.