"They need to know I mean it"

There's a belief that volume conveys seriousness. A quiet ask can be taken or left. A shouted one means business. If you don't raise your voice, how will they know that this time you mean it?

Look at how a child actually learns whether you mean something. Not by how loud you say it. By what happens next. What follows is my reasoning.

Suppose you said, quietly, "Shoes on, please, we're leaving in two minutes," and in two minutes you picked up the shoes and the child and left, with the shoes going on in the car. You've said nothing loud. Your child has learned, from one experience, that "two minutes" meant two minutes. Now suppose you shouted, "Get your shoes on NOW," and then stood in the hall for four more minutes while they finished the game. You were loud. And the child learned that "NOW" means four minutes.

Meaning it is shown by following through. Volume is what people use instead of following through, because following through is effort and volume is free. The shout is what a parent does when they haven't decided what will happen if the instruction isn't obeyed, and so are trying to make the instruction itself frightening enough to do the work of a consequence. It doesn't, because a shouted instruction with nothing behind it is still an instruction with nothing behind it, and children are good at noticing what's behind things.

This is also where threats live. "If you don't lay that table I'm taking the tablet for a week." The tablet comes back on Thursday. A threat that isn't carried out is a lesson that threats aren't carried out, and each one lowers the value of the next. Most shouting households run on a stock of threats that everyone knows are empty, and the shouting is what's left when the threats have stopped working. The way out isn't bigger threats. It's smaller consequences that actually happen, and chapter 18 is about them.

So "they need to know I mean it" is right. They do. And the way to show it is to say the thing once at a normal volume and then do what you said. After a couple of weeks of that, your quiet voice will carry more weight than your shout ever did, because it'll have a record.