7 Going On 70: A Barbara Walters Special

At birth, Lindsay showed no signs of progeria. Four months later, when she had gained little weight, her parents Kristy and Joe Ratcliffe said they knew something was seriously wrong. It took doctors six weeks to diagnose Lindsay with progeria -- a fatal disease where children on average die at 13.

"In the beginning it was a lot harder because she couldn't talk and she couldn't walk and she couldn't do everything for herself. Now, it's so easy because you see her and you smile. You can't help it," Kristy Ratcliffe said about her vibrant daughter.

(Donna Svennevik/ABC)