Joss Whedon has confirmed the rumor Crave Online reported May 3: he wants to include Quicksilver and the Scarlet Witch in his script for his sequel to The Avengers. The mutant twin children of Magneto are Avengers in the comic books, but Fox holds the rights to Marvel's mutant characters, so if they're included in Avengers 2, don't expect much talk of their parentage or the origin of their abilities.
Crave's SuperHeroHype also discovered actress Saoirse Ronan is the archetype for Scarlet Witch, but of course, no one is yet cast in the film. Whedon also talked about his view on how Iron Man will return to The Avengers.
“Well, I feel like in Iron Man 3, even though he said, ‘I’ve changed' -- he blew up his remote suits, but I don’t think anybody thinks he doesn’t have one anymore. The question is, if The Avengers are called, does he show up? And the answer is, ‘Yes!’”