I have done this lesson for many years in various formats. I have always done it with grade three as they study the solar system as one of their science units.
Some years, I have had the students create the planet spheres directly on the black paper. The focus is more on light, shadow, shape and form rather than recreating our plants.
I always discuss highlight, shadow and light source and use a flashlight and a sphere so they can see how moving the light source changes the location of the shadow and highlight.
This year, I had them create the spheres on white paper then cut and glue onto a black background. With one class, I tried splatter painting the background which worked fine but was a bit messy.
For other classes, we used white oil pastel to create stars and comets.