Use two empty tin cans with the labels removed. Half-fill one with water and ice, and half-fill the other with crushed ice and 4 tablespoons of rock salt, mixing thoroughly. Let both cans sit. Dew will form on the can without the salt, and frost will form on the can with the salt. This is because the salt actually makes the mixture colder, so the exterior of the can begins to freeze.
Make frost on a few different cans and place them in different areas around the room so the children can see which one loses the frost more quickly. Put one can in the sun, another in a shady spot and another in the refrigerator. Discuss why the results happened in basic terms, explaining how the hot sun will melt the frost more quickly because of the heat, whereas the cold refrigerator will allow the frost to stay on the can longer.
After you have completed the experiment on making frost, try to repeat the results using different materials. Use a glass measuring cup, a paper cup and an aluminum foil cup. See whether the frost appears at all, or if it appeared more slowly or more quickly than on the metal can.
Stir epsom salts into 1 cup boiling water, ensuring the mixture keeps boiling. Gradually add more epsom salts, up to 1 cup, until the epsom salts will no longer dissolve in the boiling water. Remove from the heat and stir in 3 tablespoons dishwashing liquid. Let cool. Paint the mixture onto a window or mirror and let dry. It will dry, and fan-like patterns will appear, just like frost. To remove the solution, simply wash the window with soap and water.