What happens to a family when a child's birth becomes a medical mystery? Barbara Walters reports on Kaylee Halko and Lindsay Ratcliffe, two vibrant young girls who suffer from a rapid-aging disease called progeria, a fatal condition that currently affects 80 known children in the world. The disease causes children to age at 10 times the normal rate. It is incredibly rare - occurring in only one of every four to eight million births - and always fatal. On average, children die at the age of 13.