Miri

The basic storyline was fine, with the children & virus, but there was no point to their planet being a duplicate Earth.

The environment could just as well -- and more plausibly -- have been an Earth-like planet colonized by earthlings in the very early days of space travel, and forgotten by history. Some feature of the planet could easily have accounted for the longevity of its inhabitants.

There was no follow-up or explanation of the duplicate Earth aspect of the story, and the story would have been just as good without it.