Talk with your child about the relative sizes of things, such as: small, smaller, smallest; big, bigger, biggest; short, shorter, shortest; tall, taller, tallest and so on. Begin by comparing two things: That fish is small, but is there one that is even smaller? Then, compare three or more things: That fish is small and this one is even smaller, but which is the smallest fish of all? Develop your child's visual acuity by asking him to estimate which is bigger. Estimating on the basis of what you see is a lifelong skill—one that you can begin developing now!