Make pH Paper Test Strips
This is an example of a project that doesn't require a lab or special chemicals and that is safe and easy enough for kids to do. You can make your own pH paper using nothing more complicated than a cabbage and coffee filters. My instructions involve using a blender and a microwave, but you can just as easily chop the cabbage, steep it like a tea in a small amount of boiling water, and make pH paper from the juice. You say you don't have cabbage? That's okay, too. There are many other common plants that you can substitute. The reason cabbage is most often used is because it exhibits a wide color change range.