Stereoscopic Vision
Stereoscopic Vision is your brain combining the slightly different views from each eye to see depth.
Think of it this way
Two bowls sit side by side on a shelf, each tilted toward a small ball. The left bowl faces it from one angle; the right, from another. Your brain layers both views like sheets of tracing paper. Where they line up shows shape; where they differ shows distance.
Explaining stereoscopic vision by grade level
Close one eye and look at a Magic Eye picture. Then open both eyes and try again. With two eyes, your brain blends both views into one. That blending is what lets you see a hidden 3D shape pop out of the page.