Play a whispering game with your child and experiment with what a different way this is to communicate! Agree that for five minutes you will whisper everything you say to each other.
Notice how you have to be closer together to hear what is said, and how you have to look at each other to notice if anyone is talking at all. Also notice how much louder other sounds in the environment suddenly seem to be. Can you whisper softer or louder? Can you make a shout/whisper?
For a fun extension when your child has friends over, play a simple version of the old favorite game, "Telephone." Sit in a circle and start the game by whispering a word into the ear of the child next to you. That child then whispers the word to the next child and so on until the word has gone all around the circle. Does the same word come out as the one that started? Or is it a really silly word?