Changing something from a liquid into a solid can be as easy as placing water in a freezer and making ice. Make sure to discuss that when matter freezes it loses heat and energy, the particles move closer together and slow down, and eventually the substance turns into a solid. Get the kids more interested in this experiment by changing up the matter you will be freezing. Instead of using water, freeze fruit juice in small disposable cups, add Popsicle sticks and create tasty fruit-pop snacks. Or make ice cream by mixing 1/2 cup milk, 1/2 tsp. vanilla and 1 tbsp. sugar in a 2-qt. freezer baggie. Place the sealed baggie inside a 1-gallon freezer baggie filled with 4 cups crushed ice and 4 tbsp. salt. Massage and shake the baggies. After about seven minutes, you will have ice cream. Get the kids to work in pairs, taking turns shaking the baggies so their fingers don't freeze.
Using sugar in crystal forming experiments to seemingly turn liquids into solids can be intriguing for young children. Make your own rock candy by boiling 3 cups of water in a large pot. Add 8 cups of sugar, one at a time, stirring slowly until each one is dissolved. Allow the solution to cool for about four hours. Pour the solution into glass jars, and add food coloring for colored candy. Tie a string to a piece of dowel and suspend it horizontally across the mouth of the jar so that the string hangs down into the solution. After several days, the sugar will crystallize around the string as it separates from the solution, forming delicious rock candy and a great experiment.
One of the weirdest and most jiggly foods that kids enjoy is gelatin dessert such as Jell-O. Jell-O makes an informative solid-to-liquid-to-solid experiment that will teach kids how to classify solids and liquids. Show them the powder and teach them about the pouring nature of liquids, but describe how Jell-O is a solid known as a powder that has the same ability to be poured. When making the gelatin dessert, the steam from the boiling water gives you the opportunity to discuss evaporation as well. Make the Jell-O and allow it to solidify, discussing all the different states of matter. When all the learning is over, you can have fun eating your experiment.
A substance that is both a solid and a liquid can be formed by mixing 1 1/2 cups cornstarch with 1 cup water. Combine the two ingredients and mix until the mixture is uniform. Add a few drops of food coloring if you would like colored goo. When you place the liquid goo under pressure, it becomes a solid. Once the pressure is released, the goo turns back into a liquid. Allow the kids to put their hands in the goo and squeeze, and experiment with it while you discuss the different characteristics of liquids and solids.