The Happy Nappy is one of Perfect Peter's favourite books. Milksop Miles is the author. Horrid Henry calls it The Snappy Nappy due to hating the book. Most of the characters are, literally, living nappies with a different prefix to start each name (Clappy, Yappy, Gappy).
In Horrid Henry Reads a Book one of the book reports Henry does is on The Happy Nappy and, to achieve the target of twenty seven, he makes up a Happy Nappy book series where he travels the world.