Yep. Both parents have to be citizens for a child to be a natural born citizen.
Again... source?
1. Natural born citizen is not Constitutionally defined. We do not have precedent to establish the meaning of this.
2. If natural born citizen means someone who does not need to be naturalized, then there is not and never has been a requirement for both parents to be citizens.
3 - What argument do you make for a requirement for two parents ?