Print numbers around the edge of a paper plate to look like a round thermometer. The numbers can simply range from a typical summer morning in your area to a higher number for the afternoon heat. Give a paper plate thermometer to each preschooler. Every half-hour or hour, take the children to a window or an outdoors spot where they can see a real round thermometer. Have them use a different color of crayon to color their plates over the number the real thermometer has reached. Discuss how the sun warms the earth and makes the thermometer numbers rise. Repeat the activity each day for a few days or once a week. Bring the children's attention to cloudy and cooler days to show how the lack of sun makes the temperatures lower.
Teach the children how the sun makes shadows. Have adult helpers stand a child at the end of a piece of newsprint on a hard surface. The adults should draw the shape of the child's shadow on the paper. Preschoolers can finish their picture by coloring the shadow black or gray and drawing a sun at the top of the page.
Have several shallow pans of water ready to set outside throughout the day or during class. Have preschoolers touch the water in each pan to know the water is cool. Set one pan outdoors in the sun every 15 minutes. As you set out each pan after the first one, have the children touch each pan of water to experience how much warmer each one gets after the sun shines on it for different periods of time. To further this science experience, have the children press their wet hand print onto a piece of paper each time they set out a pan of water. Help them notice that the hand print is dry or nearly dry after just a few minutes.
Have bowls of shaved crayon pieces ready before class time. Preschoolers place a piece of light-colored paper in the sun outdoors. Have the children sprinkle crayon shavings onto their paper. Later, come back to the papers. Discuss how the sun's heat has melted the crayon pieces. If you wish, have the children use a paintbrush to spread the melted crayons around to form a picture or design. You may wish to cover the dried pictures with clear adhesive plastic.