Teach children how plants absorb and distribute water with a simple celery experiment. Fill a glass with water, and add 10 drops of red or blue food coloring. Place a stalk of celery in the glass, and check it every few hours. Observe the color changes in the celery stalk and use a peeler to see how deep the color changes go. The longer the celery sits in the water, the darker its stalk will be.
Kids will quickly grasp the acidic properties of vinegar when the see its effects on the common egg. Start by placing an ordinary egg in an airtight container. Cover it with white vinegar, close the lid, and refrigerate for 24 hours. When time is up, carefully remove the egg with a spoon. The shell should have started dissolving. Dump out the vinegar and put the egg back in the container, covering it again with fresh vinegar. Place the container back in the refrigerator for another 24 hours. The next day, remove the eggs and rinse them carefully. What will be left is a "naked" egg. The clear membrane will be intact, but the hard shell will have completely disappeared.
It is easy to create invisible ink messages with your kids using lemon juice. Squeeze the juice out of a lemon and mix the juice equally with water. Dip a cotton swab into the mixture and use it to write on a white sheet of paper. Let the paper dry completely. Your message will be invisible, but it has not disappeared. Hold the message up to a light bulb or other heat source to reveal the writing. Because lemon juice is acidic, it oxidizes and turns brown when it is heated. When heated, your writing appears as though written in brown ink.
Create an intense color explosion with milk, food coloring and dish soap. Pour milk into a shallow dish. Whole or two percent milk works best. Add a few drops of different food colors, keeping them close together. Dip a cotton swab into dish soap and place it in the center of the dish of milk. After holding it there for a few seconds you'll see the colors rapidly mix and swirl throughout dish. This happens because the properties in the soap break up the fats and proteins in the milk.