My just-turned-4 year old granddaughter listened to the whole story in one sitting. She was keen to see the illustrations, but concentrated well throughout. When her dad asked her about it 3 hours later she said, “ It was fun!”. Her description of the story focused on pet sitting, Gus' escape and the chaos he caused. She has been read many books a day since tiny and loves them, and has advanced language skills, so has already listened to other 'chapter books'. I imagine some active 4-year-olds wouldn't yet be ready for this book.
Janet, Grandparent