Show kids that light is made up of red, orange, yellow, green, blue, indigo and violet. On a hot day, hold onto a garden hose with your back facing the sun. Spray water from the hose by holding your thumb over the end of the hose. Watch the water spray against a dark background until the kids can see a rainbow in the spray. Explain that light bends and slows down as it passes through the water, so you can see all the colors in the light spectrum.
Kids use markers all the time, but they may not realize that some of the markers' colors are made up of more than one color. Have the kids make spots on coffee filters with different colors of markers. Tell them to keep the colors separated. Next, instruct them to use an eye dropper to put a few drops of water on each color. Allow the coffee filter to dry. The secondary colors (purple, green and orange) will separate into primary colors (red, yellow and blue), and when the coffee filter dries they'll be able to see which primary colors make up the secondary colors.
Light refraction experiments help kids to understand that light travels through the air in straight lines. To illustrate this principle, fill a glass or clear jar halfway with water. Place a pencil in the water. Have each child look at the pencil from the top and then look at it from the side. When they look at it from the side, the pencil looks bent. Explain that light travels through water slower than it travels through air, so as the light enters the glass of water it slows down. As the light leaves the glass it speeds up again, making the pencil look bent.
To help kids understand the importance of roots to plant growth, fill a glass half full with water, cut the end tip off a carrot and insert the carrot into the glass. Place the glass near a sunny window and have the kids observe it for several days. Tiny side roots will begin to grow along the sides of the carrot. Explain to the students that tree and shrub roots work just the same way. Their roots grow out sideways to increase stability and to search for water and nutrients.