An acquaintance at Ari's school actually knows these precious girls and sent around a link to their personal website. The girls, four-year-old twins Addison and Cassidy Hempel, suffer from a rare pediatric case of Alzheimer's disease known as Niemann-Pick Disease Type C. The vast majority of children with the disease die before the age of 20, according to a recent story by ABC News:

"You can't tell your kids they're dying," said a sobbing Chris Hempel, Addison's and Cassidy's mother. "They'll never know."

The Symptoms and Signs

The Hempel family didn't always carry this burden. When the girls were born, they were healthy and hitting all the major milestones.

By their first birthday, they knew how to walk, but soon the girls' parents knew something was wrong.

When Addison and Cassidy were two years old, they caught a viral infection they couldn't shake. Scans showed each girl had an enlarged spleen, but doctors couldn't determine the cause. Then, things began to get worse.

"I started seeing increasing symptoms with balance and coordination -- bumping into walls and falling down," Hempel said. "And when they were around other kids, I noticed they weren't running as quickly or jumping. I started getting really concerned."