It's "Next Avengers," the latest straight-to-DVD movie from Marvel. In a nutshell, thirteen years before the story started, the Avengers were mostly wiped out by an AI called Ultron. Now their kids, who have grown up under the care of Tony Stark/Ironman, have to go up against Ultron themselves.

The concept sounds like an AU fanfiction. But it's just so *good*! ^_^ Even if the end of the last battle is something of a dues ex machina.