Use two round balloons that are not inflated. Inflate one balloon with air and tie it closed. Pour 1/4 cup of water in the other balloon, inflate it the rest of the way with air and tie it off. Strike a match and place it under the first balloon and record what happens. Strike another match and place it under the second balloon with the water in it and record what happens.
Use different sizes, types and shapes of balloons to test the splatter factor. Fill the balloons with water, and stand on a ladder. Drop the water balloon to the ground, allowing it to splash. Measure and record the diameter of the splash to determine which balloon provides the greatest splash size. Try dropping the water balloons from different heights.
Give each student in the class five large balloons with a jar that has a 5 cm top opening. Fill the balloons with water and have one student hold the jar while the other student tries to shove the water balloon into the jar. After several unsuccessful attempts by each student, hand them a 6-inch square of newspaper that is folded like an accordion so it'll fit in the jar. Light one end of the newspaper with a match and drop it into the jar. Holding the balloon by the knotted end, place it over the opening of the jar and watch as it wriggles into the jar.
These experiments deal with some hazards, such as fire. Take all of the appropriate precautions. Water can be messy, and can cause slips and falls.