The Okines, the Ratcliffes and the Halkos hope that the ongoing clinic trials and research will unlock the secrets to their daughters' medical mystery and the process of normal aging.
"The evidence is growing, that the same glitch these kids have that causes them to produce a protein that makes their cells unable to keep dividing, that same protein is being produced by all of us," said Collins. "It looks as if this maybe part of a program that prevents humans from being immortal."
Every year, the three families raise money for the progeria research, typically through walk-a-thons.
Kaylee is very aware of the high cost of research and participating in clinic trials. She told Walters her wish is to, "that I have thousands of dollars to buy my medicines."
The families all say there is no preparing yourself for the probability that you will outlive your child.
"It scares me. Not much scares me, but that does. Even thinking about it [scares me], so I generally don't allow myself to go there," said Joe Ratcliffe, who tattooed the Progeria Research Foundation's logo of a child's handprint and dove on his arm as a symbol of hope. "That's what we fight for. Without awareness we have nothing."
"20/20" first met the girls last year and caught up with them again this week. They continue to be determined to enjoy life, however short it may be. For Lindsay, her first trip to the beach was a brave new world of discovery.
"She saw the ocean and was just in awe of all this water," recalled her father, Joe.
Lindsay is usually unable to stay in the water for more than ten minutes. Due to progeria, she has very little body fat and cannot tolerate the cold. But her parents came up with an ingenious solution -- a wet suit -- specially tailored for her small size. Lindsay was ecstatic when she saw it.
"Making a big deal out of things that are big to her is just going to make her happier," said Kristy. "We just want to make sure she has as much happiness as she can hold."
This summer, Lindsay, now 7, returned to the beach, swimming freely thanks to her wetsuit.
Hayley is enjoying school and despite her size has many friends both in class and around the world. Recently, her dream came true, when she met her idol Justin Bieber thanks to a Twitter campaign.
Kaylee, too, is enjoying public school and is preparing to enter the second grade in the fall. Her mother Marla was afraid of her riding bus alone but not Kaylee, with her enormous backpack on her tiny frame, she took one small step towards education and one huge leap into her future.
She is now taking hip-hop classes and dreams of starring in her own television show.
Kaylee has advice for all the children who share her disease: "Be fabulous. Don't let one thing ruin your life!"