Her name is Ruby. She is four years old. Like most children that age, Ruby loved to run, sing, dance, and play. But she started complaining about pain in her knees. Ruby’s parents took her in for tests. The results were shocking—a diagnosis of cancer, stage 4 neuroblastoma. Ruby was in trouble. She was quickly admitted to the hospital.

Ruby’s hospital stay lingered on, spilling over into the Christmas season, a hard time to be away from home. One of Ruby’s nurses came up with the idea to place a mailbox outside her room so family could send letters full of…