6-year-old Jack and his baby sister Everly are the best of friends.
Everly has a congenital heart condition that affects one in every 100,000 babies. She basically has half a heart, which means her body has to work really hard just to keep blood and oxygen circulating through her body. At just 7 months old, she's already had two major open-heart surgeries and is scheduled to have another this summer.
Screenshot via Starlight Children's Foundation.