The Griffin of Greed by Diana Kathryn Plopa
This children's fairy tale teaches the importance of community cooperation and forgiveness as paramount to a fulfilled life, instead of collecting "stuff". This story will have children becoming more inclined to share their toys with friends and siblings, alike.
** Fun Fact: This is one of the stories that Thomas writes back to Gillian in "A Tryst of Fate".
(reworked for a young reader, of course).