The Wind in the Willows is an acclaimed children's book by Kenneth Grahame, published in 1908. Like many books written around the turn of the century, it is very much a product of its time.
At its core, Willows is an adventure story, told about brave heroes and cowardly villains. The stories were originally told by Grahame to his four-year-old son, and so reflect the sorts of things a male child of that age enjoys; car chases, capsized boats, last-minute rescues, and the heroes always triumph and return to their homes. The most important female role in the book is not even a female character, but a disguise that several characters use to get in and out of sticky situations. There is a barge-woman of indeterminate species, but she exists solely to throw Toad into the river when she discovers his uselessness. Moreover, the jailer's daughter, in her empathy for Toad's plight is the one to organize Toad's escape from jail, but her altruism is equaled later by the railroad conductor.
At the time of publication, Woman's Liberation organizations around the world were taking root. The accepted roles of women in society were being redefined, and Grahame's marriage was a troubled one; it is possible that by not including females in the story, Grahame was unconsciously remarking on a world where women didn't live at home and do the washing, but didn't exist at all and so caused no strife. Again, this attitude towards women is typical of the era, and should not necessarily be interpreted as it would be today.