He started writing about Spot the playful puppy in 1976 for his little son Christopher. In that first book, Spot was hiding behind little flaps which could be lifted by small children, an innovation which he devised. Hill said that he aimed to recognise "that children have far more intelligence and style than many adults credit them with", and to invite them to experience "ideas which were just outside their experience yet were basic enough to be understood. " He went on to say "In Where's Spot? I thought it would be fun to draw a chair—in a period style rather than a straightforward type. A grand piano instead of an upright—pink rather than brown. Tables with cabriole legs and other decorative details. All to broaden the visual scope that a book can bring to a young mind. "