If there is one thing Bardin's book is not, it is a children's book. But that is exactly what this awful alternate cover, with its cutesy horse, makes it appear to be. (In fact, this is the cover of the first edition. Perhaps this explains, at least in part, the poor performance of the book on first publication.)
This more familiar cover, featuring a Salvador Dali painting, appeared after the Brits started making much of the book's psychological elements.