Note how size relationships create depth or space in a composition. Children in first grade can already recognize closer and farther based on size even though they wouldn't typically use this in their pictures unless they were motivated to do so. Repetition can be used on all of the Visual Elements. If things are repeated without any change they can quickly get boring. However, repetition with variation can be both interesting and comfortably familiar.
Repetition gives motion.
Variation can be used with all of the visual elements. You can do this with all the elements. Artists do this all the time. Most second graders can see this effect when they are asked to look for it. These butterflies create the illusion of depth even though they are all the same size.