It's important to design simple experiments for kids. Avoid complicated microphone and recording set-ups, and provide step-by-step instructions for setting up equipment and conducting the experiments. Instructions should include ideal volume settings to avoid distorted signals. Children should also be taught how to care for microphones and recording equipment to avoid damaging gear. Make adjustments to microphone experiments if you don't have access to certain types of microphones or recording hardware.
Connect two shotgun microphones to separate field recorders. Set up something that is capable of creating a noise that can be heard from far away, such as a hammer hitting a metal barrel. Press record on both field recorders simultaneously. Record the barrel with both microphones close to the noise. Continue recording and move one microphone 100 yards away, then 200 yards away, then 300 yards away. Listen to the recordings at the same time and observe how the noise appears later and later on the second recording as the microphone moved away from the noise. This experiment will introduce kids to the idea of the speed of sound, which is approximately 372 yards per second.
Set up a field recorder on the side of a road with a microphone pointing at incoming traffic. Record cars as they drive past. Listen to the recordings and try to determine the point at which the cars drive past the microphone. The cars will have higher frequencies as they move towards the microphone, and lower frequencies as they drive away. This is called the Doppler effect. The frequency of the car noise is not changing, but the frequency appears to be different when the sound is decreasing or increasing in distance from the listener.
Record someone talking or singing loudly in a small classroom or office. Set up the microphone away from the speaker so that the room sound is recorded. Record someone talking or singing in a school gymnasium. Again, place the microphone away from the speaker. Listen to the recordings and compare how short or prolonged the sound of speech is. This experiment will introduce students to the idea of sound waves reflecting off walls and continuing to be audible depending on the size of the room.