The Shrinking of Treehorn

Blurb

The Shrinking of Treehorn is a book by Florence Parry Heide, illustrated by Edward Gorey and first published in 1971. The main character in the book is Treehorn, a young boy who begins shrinking in height after playing a strange board game. Treehorn's parents fail to notice.
The sequel to this book is Treehorn's Treasure.