Originally Posted by spideyboy_1111
In the comics its both though. Waiver even states on film "most powers manifest at puberty" key word... "most" . Charles, Raven, and Kurt in the comics were always told to have been born with there abilities. The movie series obviously gave movie xavier and mystique that same trait
But Magneto is a very intelligent and well-informed mutant. The fact that most mutants develop their powers well after birth would be enough for him to realize that the baby Mystique just conceived could likely be a mutant.