I used clean and dry soda bottles and filled each bottle with various magentic items (cut up pieces of pipe cleaners, brads, and paperclips). I use magnetic wands with mine, but any magnet would do. You could add any type of magnetic materials. When discussing magnetic vs. nonmagnetic materials, you could add items that aren't magentic for the kids to experiment with. Let them help you find items to place in the bottle. This is a safe, choke free way to discuss magentism when little items are involved. And the items can be easily changed to keep them interested.