Silver-Haired men=obviously clones born from Make Energy.
the children=you probably noticed the "children" stuff in the movie. I think it comes from when Sephiroth died, the power he had was then recycled by the lifestream and given to the children born after the happenings of Sephiroth. Remember that Bugenhagen said that Spirit Energy is recycled by the Lifestream? Think of the children as Sephiroth spread out through a large number of people.