The Berenstain Bears and the Trouble with Friends by Stan and Jan Berenstain
The Berenstain Bears stories, by Jan and Stan Berenstain, are a series of popular children's books that teach kids moral lessons in an entertaining way.
This one shows kids how to get along with friends and keep a friendship - a humorous story that teaches life lessons in a way that kids can relate to, and remember easily. Non-preachy, and pure fun to read.