With raisins and soda water, you can teach preschoolers all about carbonation while entertaining them at the same time. Take a bottle of soda water and a handful of raisins. It works better if the raisins are fresh. Talk to the children about soda water and what makes it bubbly. Then open the bottle, and add the raisins. Everyone can watch as the raisins dance while bubbles collect around them. Then close the lid, and watch them stop. Ask the children why, and explain it is because of the nature of gases and the bubbles getting stuck in the crevices of the raisins, causing them to float.
An activity with magnets is a great way for youngsters to learn about the laws and rules of magnetism. With two chairs or benches or blocks (something that will offer support) and a thin sheet of plexiglass, set up a station for preschoolers to learn about the power of magnets. Let everyone in the class have a magnet or share a magnet, and then have them come over to the station to pick out pieces of metal that will work with their magnet. Then have have them set the piece of metal on the plexiglass and place their magnet right under it. By moving the magnet, they will move the piece of metal. This can also be done the opposite way, showing them how their piece of metal will hang upside down with the magnet above it.
You can perform an experiment with an empty 2-liter soda bottle, a balloon, baking soda, vinegar and a spoon to teach your students about observation and prediction. Fill the 2-liter bottle half way with vinegar, and then place as much baking soda as you want in the limp balloon. Place the end of the balloon over the 2-liter bottle of vinegar, but don't flip it yet. Ask the youngsters what they think will happen to the balloon before you flip it. You can do variations of this with different sized balloons and amounts of baking soda. Explain why the balloon fills up and ultimately pops.