My son did pinhole cameras for his science fair project last year. We just used a modified body cap on a 35mm camera and tried different sized pinholes to see what effect they had on the image. We also took some non-pinhole photos and compared the properties of the "lens" images to those of the pinhole images.
Not sure what the requirements are for your son's science fair, but be sure to delve into the science of pinhole cameras. Most school science fairs are looking for more than just pretty pictures and want the student to understand (and be able to explain) the science behind them.
I've been into pinhole photography for about three years and there's just a certain magic in making an image with a camera that costs practically nothing and has no lens. Hopefully this project will ignite your son's interest in photography. And don't forget about Worldwide Pinhole Photography Day, April 30th. See http://www.pinholeday.org for more details.