The tone of this excellent children's book (which yet has so much to offer for adults) is playful, reverent and passionate. This of course mostly comes from the dominance of the Mole as one of the central characters. The novel in a sense explores Mole's friendship in the new society he has joined and the various "ecstasies" he discovers as he experiences more and more of river life. Note the following quote that describes Mole's enjoyment of river life in the very first chapter:
Absorbed in the new life he was entering upon, intoxicated with the sparkle, the ripple, the scents and the sounds and the sunlight, he trailed a paw in the water and dreamed long waking dreams.
Such quotes expressing Mole's enjoyment of life and his playful, childlike enthusiasm, dominate the novel, expressing perfectly the playful and passionate tone of the text, which of course allows Grahame to use animals as characters to explore human feelings and emotions.