I've always been drawn to and fascinated by physical and psychological change. If I'm able to make pictures of children that are so real, as you follow the children over the years in any given book, and in subsequent books they get older and older and grow up, perhaps there might be something cautionary in that visual example. Every child is going to grow up. You can see it happen in the books: They get older and older and belong to themselves to a greater and greater extent.