Apples and Handwashing: "We put a clean apple slice in one jar. We passed another apple slice around the class as we came in from recess with dirty hands. We have been observing the two jars in the science center. This is the difference after 8 days - gross! (This picture doesn't really show the mold.)" - A great way to teach about germs.
Solar System: Rotating and Revolving Teaching Special Thinkers. I would use this to teach the difference between the planets rotating and revolving. After this, I could work my way into the stars and different constellations.