Most preschoolers enjoy creating art projects, and using balloons will be an interesting change from using only paper and crayons. Children can paint on inflated balloons or tape on pieces of paper to turn them into creatures. For instance, tape two paper feet to the bottom of a balloon and paper eyes to its front to create a balloon person. These activities will teach children to see how many creative things can be done with a simple balloon.
If you keep balloons on hand, they can be turned into a game in a pinch. Blow up balloons and ask children to see how long they can keep the balloons from touching the ground. They may use their hands or heads to bounce the balloons, or blow them upward to keep them afloat. Children can also try to play catch with an inflated balloon. They'll have to learn to be gentle so it doesn't pop, and they may be amused by how hard it is to make the balloon go where they intend it to go.
Although children have surely seen a balloon be inflated, they probably don't think about what's happening to the material of the balloon when it's being blown up. Demonstrate this concept to children with an art project. Partially blow up a balloon with a few breaths and hold it closed while children gently draw on it with markers. Finish blowing the balloon up and ask children to describe what they see. They should realize the drawings gets stretched and move further away from one another as air enters and the material gets thinner.
Since children can't see air leaving a balloon, they may not be able to picture what's happening when a balloon deflates. Demonstrate this concept with a fun experiment. Place one end of a bendy straw through the opening of an inflated balloon. Keep a finger over the end of the straw so air doesn't escape while you attach a rubber band over the opening to keep the straw in place. Place the balloon on a table and remove your finger. The balloon should move across the table as the air escapes, demonstrating how quickly the air is leaving the balloon. Refill the balloon and let children experiment with how it moves when they bend the straw in different directions.