Octahedron facts for kids
Simply put, this is two rectangular pyramids put together. A rectangular pyramid is a pyramid with the base of a square or rectangle. In other words, this is just a pyramid that, when flipped to stand on its point (like a spinning top) it has a rectangular from a birds eye view.
Images for kids
Two identically formed rubik's snakes can approximate an octahedron.
Octahedron Facts for Kids. Kiddle Encyclopedia.