As with most quality science experiences, the materials are simple (water, wax paper, toothpicks and food coloring), but the science learning is complex. Look at the concentration on this child’s face.
On wax paper, water will bead up into a dome. Water will cling to a finger, straw, or toothpick and can be led around to join other drops and make big drops or break large drops into smaller ones.
Try placing a simple maze underneath and challenge the children to move the water through it, or try moving the water in other ways such as shifting the paper or blowing on the drops. Use different colors of water so they can join the drops to mix colors. Try drops of other liquids such as oil or soap, and see how they are different. Try drops of water on other materials such as regular paper, aluminum foil or fabric and see what the water does.
This type of activity engages children, because water is something they are so familiar with and yet in this setting, they are surprised by what it can do. By providing a variety of materials to explore, you can use the same basic activity but add something different everyday to extend the learning and deepen the understanding.