The Little Folks' Book of Flower Fairies
Mentioned in The Light Fantastic, this is a book about pixies that Twoflower read as a child. It gave him what, even on the Discworld, could be described as some dangerously naive ideas about the nature of, for e.g., Elves. Buggy Swires was moved to tell him that this didn't sound quite like the sort of elves we get round here...