At least in Indiana, sound energy is studied in third grade science. I've enjoyed teaching our hands-on sound unit the last few years. When we talk about sound waves, I like to show some videos of "Ruben's Tubes". A Ruben's Tube is a tube with tiny holes in a straight line along one side. The tube is filled with propane and sealed at one end. The other end has an audio speaker. Tiny amounts of propane leak through the pinholes. The propane leaks are lit and little flames appear at each pinhole. Sound waves are compression waves, so gas particles are brought together and pulled apart as the sound energy travels, so when a sound wave travels from the speaker through the tube, gas particles become condensed in some areas (producing a higher flame) and sparse in other areas (producing a lower flame). This makes for a really cool sound wave visual.
The first video I've shared here is my favorite of the Ruben's Tube videos. The second is a scene from the T.V. show "Mythbusters".