Like any other skill, controlling voice volume takes practice. Practice should take place in a relaxed, accepting environment - so, at home or school and not in the grocery store or restaurant. I'm not suggesting you shield your child from public until they are able to properly label and produce a decrescendo or crescendo. By playing games, doing activities that require producing sound, and direct instruction you can practice volume control.
Visuals work great for children. We created a visual that includes colors, words, and pictures to represent different levels of sound. Since I work with young children, I chose to exclude "silent" because that doesn't come up much around here. What we did include on our volume scale was:
Indoor Voice / Talking Voice
On yellow paper (because it is calm and happy and we have yellow walls inside), we defined an indoor voice as talking with a calm body, loud enough so the people next to you can hear you. We also identified activities we could do while talking, some included playing, taking turns, circle time, and singing songs.
Outdoor Voice / Playing Voice
On green paper (because many plants are green), we defined an outdoor voice as talking loudly so people who are near or far can hear you. Your body might be moving a lot, but you are in control of your body and being safe. We identified activities you could do while using an outdoor voice: playing a game, racing, riding bikes, talking to a friend.
Emergency / Yelling or Screaming
On red paper (because fire trucks are red), we defined an emergency voice as screaming or yelling. Your body might be calm or moving a lot and you might not be making safe or caring choices. The sound is so loud that it hurts people's ears, especially when they are close to you. We identified times that would be appropriate to use an emergency voice: someone is hurt badly enough to go to the hospital, there is a fire, someone is trying to take you away without mom or dad's permission.
We also discussed that the screaming voice is just to get attention for help, so that when we are fixing the emergency or waiting for help we are able to focus. For example, we wouldn't scream when the fire alarm went off, because everyone can hear it and we know that means there is an emergency.
These scenarios were touched on lightly, as I don't want children to become anxious about it happening. I sum it up in real time by saying something along the lines of, "Ow. That was too loud. Do you need help right now? Is it an emergency?" and that is enough for them to understand.
If you have a child that is having a difficult time understanding, keep the visual posted where it is most handy for you. I keep mine in my circle time area because that is normally where we practice. Note: When I say "visual" I am simply referring to a poster or piece of paper with pictures and words on it.
Chances are if you have young children, they are doing these types of activities all the time. A classic favorite is beating on pots and pans. This is a time you can catch a child in the moment and discuss volume.
*Bold means loud, italics means regular talking
When a child is playing and making sounds, join their play. You can ask questions that influence them to think about volume. "Wow. That pot is LOUD. It reminds me of a fire truck going to help someone."
"You have your doggy? He is so fluffy. And he barks? Oh, he is barking softly because we are inside."
You could also do modeling while playing. Modeling means you, the adult, purposefully do an action so that the child can observe and, hopefully, think about.
(while reading) "Froggy yelled to his dad - WWWHHHAAATTT!?"
(during a transition) "I'm walking inside now, it is time to speak with an inside voice."
(baby dolls are in their bed) "Shh. The babies are sleeping. They need to sleep so we can play more later."
Again, while playing, you can purposefully do the wrong thing and hope that the child points out your mistake. It may be best to do this first with another adult present, who can point out the mistake. Sometimes a bit of play acting by adults helps children understand.
Big Little Silly is a game that I made up that was influenced by a music lesson. I don't remember the music lesson now, but the jest of the game is to follow directions (hah! that will be another blog post) and control your voice volume.
Big Little Silly is conducted using hand gestures and, if needed, spoken directions. You may consider using a cue cards as a visual, depending on your child's needs. The rules are that there is no screaming, because then the teacher would think there is an emergency, thus causing the game to stop.
For Younger Children
I only do Big and Little until the end, because once they are silly there is no turning back.
For Older Children
Use your best judgement. Sometimes kids can handle going from silly back to calm and other times the same group of kids can hardly stay in one room.
Well, now that you are actively conversing about volume, your child will have some idea of context when you tell them they are too loud or need to speak quietly. This is something that needs to be practiced repeatedly for most kids, at least the ones I have met. I think the most important practice should be done while playing. That will give the kiddos a warm fuzzy feeling when you are telling them in real life that they need to use an inside or outside voice. They will be more comfortable with it. And comfortable is good, right?