The Metal Campfire

Three kids, two boys and one girl out in the middle of a desert that used to be New York and now is only ruiens, it's very warm out and their used to cold tempetures underground. They're searching for the reason why the land turned barin and humans where forced underground and won't accept their parents explination that evolution made them go underground. But it dosn't make sense since the three children feel that they NEED to be out of the ground. But what they find explains why the dead arn't buried.