One of the best ways to show preschoolers how easily germs can spread is to make germs visible. Coat your preschooler's hands in flour and explain that the flour represents the germs that are on her hands. Give her a toy to play with, such as a wooden block or some plastic animals. Set a timer for 10 minutes and encourage the child to play until the timer goes off. You will notice that the toy is now coated in flour. Have the child wash her hands in the sink with warm water and soap. When her hands are dry, have her play with the flour-coated toy again. Point out that her hands are, again, coated with flour, or germs.
This is a messy experiment, but it can easily show children how germs can be transferred from one person to another through touching and sharing toys. Dress each child in clothes that can get dirty, or provide smocks for each child. Lightly coat one child's hands in cooking oil, and explain that the oil will represent germs. Have the child shake hands with a friend. Have the friend shake with another child, and continue the hand shaking throughout the whole class. Each child will now have some degree of oil on his hands. You can also give the first child with the oil on his hands a plastic cup or toy and have him share it with a friend, who will then share it with another friend and so on. This will show that germs can spread on toys and other objects, as well as through hand-to-hand contact.
Explain to your preschoolers that some germs, such as those from sneezes or coughs, spread through the air instead of on your skin. For this experiment, you will need some confetti and a table fan. Place the confetti on a table in front of the fan. Tell the children that the fan will simulate a sneeze or a cough and the confetti are the germs. Turn on the fan and watch the confetti germs spread throughout the classroom. Have children stand near the fan and see how many pieces of confetti, or germs, can affect them.
Once children understand how easily germs can spread from one person to another, it is time to show them how to prevent the spread of illness. The best and easiest way to prevent germs from spreading in a preschool classroom is through regular hand washing. Encourage children to wash their hands upon entering the classroom, before and after meals, after using the bathroom and after being outdoors. Sing a simple song such as "Row, Row, Row Your Boat" in order to encourage children to wash for an appropriate amount of time.