Sinking and floating is a basic scientific exploration for preschool children. Gather items of various sizes, shapes, weights and densities. Fill a fish tank or other clear container with water. Explain to the children that they are assisting you in an exploration of items that sink and float. Present the first object. Pass it around so each child can feel it. Ask for predictions on whether the item will sink or float when place in the container of water. Probe the children to understand their reasoning for the prediction. Place the item in the water and compare the results with the predictions. Continue the exploration until all items have been explored.
Use paint to explore how colors mix to create new colors. Give each preschool child a small amount of red and blue paint. Encourage the students to mix the colors and observe the results. Repeat the process by giving each student a small amount of red and yellow paint and then blue and yellow paint. Make a group chart to show the resulting colors made from mixing each combination.
White carnations and water dyed with food coloring demonstrate the way water is drawn through plants. Mix a few drops of liquid food coloring with water. Repeat for as many colors as you wish to create. Have the preschool children assist you in placing white carnations into the containers of colored water. Observe the petals of the carnations each day. Ask the preschoolers to explain what is happening to the flowers. Take a photograph each day of the carnations so you can see the color progression.
Baking is a delicious way to demonstrate chemical changes to preschool children. The concept of chemical changes is advanced for preschoolers, but they can understand the idea that the baked goods cannot return to their previous state once they are removed from the oven. Select a recipe for a baked item such as cookies, cakes or bread. Divide the preschool children into groups. Assist them in combining the ingredients. Make observations about the batter or dough that results. Bake the items, and observe how they have changed.