how could you convince a small child that when you speak it is not necessary for air to travel from your mouth to the ear of a listener?
Sound is a form of mechanical wave which requires a medium to propagate. It travels in such a way that particles of the medium travel to and fro about their mean positions and during collisions with successive particles, energy gets transferred. The medium particles return to their original positions after the energy transfer (sound energy) takes places. Thus, the energy disturbance gets propagated further along.
In this way, sound produced upon speaking travels from the mouth to ear without the actual displacement of the medium particles or the medium (air) itself.