Picking up on something Brian Jones said at the summer AAPT meeting, I'll say that experience comes first. He described how students, allowed to play with florescent sheets and various colored LED's gain understanding from that experience. When asked specific question about light and energy later they have a sense that blue light has more "something" than red light.
When working with some 4th and 5th graders I've enjoyed explaining how balance works. A few simple tricks (like trying to stand up from a chair without leaning forward) show them what they already know. What they learned as a very small child was that it you want to stand up, you have to keep your feet under your center of mass. Even if they cannot describe it in those physical terms, they already know it.