Children's Books:
* The "Little Bear" series: He wrote many of the popular "Little Bear" books based on the original stories by Else Holmelund Minarik and illustrated by Maurice Sendak. These include "Little Bear's Friend," "Little Bear's Visit," "Little Bear's New Friend," and "Little Bear's Mother."
* "The Book of Animal Nonsense"
* "The Book of Silly Rhymes"
* "The Book of Funny Sayings"
* "The Book of Fun and Games"
Young Adult Fiction:
* "The Worst Witch" series: He co-wrote several books in the popular "Worst Witch" series with Jill Murphy, the original author.
* "The Ghost of Thomas Kempe"
* "The Curse of the Cat's Eye"
He has also written for television, and his work has been translated into many languages.