Solar system.

As S and I wandered the aisles of Hobby Lobby to find Mommy and H, we walked past the section with styrofoam balls in all sorts of sizes. S paused, then asked if he could get a few different sizes. They were all of $1.49 a bag.

"Yeah, what do you want to do with them?" I asked. "Make a solar system," came his reply.

The next day, he sat down at his desk and made his solar system. Apparently this is what he envisioned when he saw those little white balls. 

It even includes the Kuiper Belt next to Neptune (the piece of paper).

Without stopping there, he also started drawing the 3D model he had made. Notice how Earth has its moon.

That kid is awesome.