So a microphone works as follows. Sound waves strike a surface, causing the surface to vibrate. The surface is attached to a magnet inside an electric coil. As the magnet vibrates, it creates electric pulses in the coil. Those electric pulses are then sent down a wire, until they can either be converted to digital data or reach a speaker–which is basically a microphone in reverse.
This would be, for a children, a good opportunity to learn scientific facts: that sound is a series of compression waves, with the frequency and amplitude determining the pitch and loudness of the sound. Also that electric current is generated by moving a magnet with a coil of wire (i.e. Faraday’s Law). So now I’m wondering, what other ordinary stuff makes a good physics or chemistry lesson?