This was a fun little project to do with my son. He enjoys watching and playing with Planet Heroes, so has become interested in knowing more about the planets.
I got the kit to make this at a yard sale, but it could easily be replicated with some card stock , a hole punch, and some yarn. We colored and put on the planets in order (with the sun in the center), so he could learn what order they are in. He can recognize all the names of the planets now, and knows which ones have rings. I've explained to him before how Pluto is not really a planet, but he told me, "It is round and in space, so I call it a planet." So there is the scientific definition of a planet from a 4 year old.