A few more things...
1. I think it's important to help students understand the difference between rotation and revolution. Show them models, have them draw pictures, make it as concrete as possible - no matter how simple. For example, have the students stand up and make a large circle around the classroom while you stand in the center. Tell them that you are the sun and they are the earth. With their bodies, they need to show rotation (spinning in place) and revolution (walking around you). Then have them put it together and ask questions like which movement causes day and night, which movement causes the seasons. Their answers should be shown with their bodies. Review rotation and revolution every lesson. Be sure that they know that its the earth's revolution AND tilt that causes the seasons.
2. You could always use a globe and a flashlight. Put a marker where your state is on the globe and show rotation and revolution. The book "What Makes the Seasons" by Franklyn M. Branley is a great one to use along with this lesson (it even has a demonstration idea using an orange, stick, and flashlight).
3. This is a great link/video to help show what causes the seasons: http://www.youtube.com/watch?v=DuiQvPLWziQ
. However, since it is on YouTube, it might be 'forbidden' to show at school but it would give you a great explanation for yourself. And here is another link/lesson: http://www.fi.edu/time/Journey/JustInTime/seasons2.html
Similar to the second idea I mentioned.
That's all I can think of off the top of my head. Have fun!