For a simple scientific experiment, give each child one ice cube inside a clear sandwich bag. Ask each child to try to make his cube melt. Children may choose to heat the cube with their hands, blow on it or run it under tap water. Once each child has worked on his cube for about one minute, ask everyone to look at all the cubes and see what method has worked the best. Explain that a broken cube will melt fastest because it has more surface area.
Create your own ice cube paintbrushes. Fill ice cube trays with water, mixing a teaspoon of powdered tempera paint into each cube compartment. If your preschoolers tend to put things in their mouths, use food coloring instead. Cover the tray with foil or plastic wrap, then poke a wooden craft stick into each cube. This will help sticks stand up. Freeze the trays overnight. Give each child a frozen paintbrush, a pair of gloves to protect his hands and a piece of white paper to use as a canvas for his ice painting.
Explain that you're going to do an experiment to see if you can slow down the melting of an ice cube. Talk about what speeds up melting, like heat. Put out cardboard, plastic wrap, foil and paper along with tape and string. Ask each child to design a creation that will keep an ice cube from melting quickly. Once each child is done, put one ice cube into his creation. Place another cube in a bowl next to it. Every few minutes, children check on their experiments to compare the rate of melting between the experiment and the control cube.
Demonstrate how rain is formed. Fill a clear jar or bowl with hot water, then wrap plastic wrap tightly around the top. Place a few ice cubes on top of the plastic wrap, then have children get down and watch inside the jar to see what happens. As the hot water evaporates, warm water vapor will rise up. When it touches the cold plastic, a cloud should form under the plastic. "Raindrops" will then fall back down into the water.