Investigate the science of sound with your child.
Sound is vibrations that travel through a sound carrier, like air or water, to your ear. Investigate with your child what causes sound to be higher or lower. Have your child hold the opening of the large jar to her mouth and hum into it. Then have her hum into the small jar. Ask your child to offer her explanations for the different sounds produced by the two jars.
Guide her in understanding that the pitch of a sound depends on how much room the sound waves have to travel. In the large jar, the humming produces longer sound waves, and the result is a lower, deeper sound. In the small jar, the humming produces shorter sound waves, and the result is a higher sound. Experiment with other empty jars to see what kinds of sounds they produce.