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. By the third grade, most children can reproduce effects like this that they observe in nature if the teacher has them observe these effects in the landscape. Atmospheric perspective causes colors and shapes to get blurrier and foggier in the distance. Overlapping is often used by artists to create depth.
Young children try to avoid overlapping in their work.
By first grade if asked, most can explain how overlapping makes some things look closer and other things farther away. When we analyze artwork we offen start with visual effects. We notice something happening. Then we try to figure out why it happens. Motion isn't a principle.