The peerless power of Magneto has turned the smallest fountain pen into a hurtling projectile! I guess by throwing it!
This is from Avengers #49, probably a decade before somebody decided to make Magneto a sympathetic bad guy. He's still a straight-ahead villain here, all tying people up and building perpetual-motion devices and whacking poor Toad around. There's no civil rights allegory here, just a blustering, over-the-top bad guy. Anyway, he's kidnapped Quicksilver and the Scarlet Witch so as to convince them to rejoin his Brotherhood of Evil Mutants (incidentally, going into the United Nations, as he does here, and making demands on behalf of anything with "Evil" in its title doesn't give you much bargaining leverage). Wanda and Pietro, at this point, aren't Magneto's kids as far as anybody knows... he just wants some sidekicks that aren't the Toad.
I'm not sure when the relationship between Mags and his kids was revealed, but there's no way in Hell it was intended to be that way originally. I mean, they're being written by Roy Thomas, here. Seemed like his favorite thing was filling in plotholes left by Stan Lee's incredible attention to detail. If a lettering error had Magneto accidentally call Quicksilver "son" in one panel in 1963, you'd better believe Thomas'd have Pietro being followed about by thought bubbles wondering about his parentage every time the Master of Magnetism showed up. They'd get less and less subtle over the course of a single issue until he'd be thinking things like "it's HORRIBLE, but it's the ONLY THING that MAKES SENSE! Magneto - THE EVILEST OF EVIL MUTANTS -- MUST be my --- FATHER!"
And then, somehow, the next issue would opening on Quicksilver and Hawkeye having an argument and Hawkeye would yell something like "well maybe you should call your DADDY, THE SUPER-VILLAIN!" because Pietro's thoughts had, at some point between issues, been vocalized and accepted as fact.