I’ve done this before.
I laid down a lot of paper towels on a table, and got out a loaf of (cheap) bread, a small tub of butter, a small jar of jelly, and a plastic butter knife.
I said to the kids, “How many of you think computers are smart?” Most of them raised their hands. I said, “Computers are really dumb. People are smart. You have to tell a computer everything. It doesn’t know how to do anything. I’m going to show you what I mean. I’m going to pretend I’m as dumb as a computer, and you guys tell me how to make a sandwich.”
And when the first kid said “open the bag of bread!” I ripped the bag apart and let bread fall randomly all over the table. That got a lot of giggles. I continued to take the kids literally at their words until they learned to give short, specific commands, and eventually we ended up with a butter and jelly sandwich. There was a lot of laughter but they came away understanding, at least a little, what a programmer does for a living.
(I should note, I’ve also done this demonstration with adults in an “intro to programming” class, and it works just as well with them.)