I've been saying shhhhhhhhhh to Charlie a lot lately, and he's been getting quieter. I wasn't sure if he knew what it meant, but then the other day he fired back at me, "Stop shushing me, Daddy!" So I guess he figured that one out at daycare or something.
The best trick I have for keeping him quiet is to whisper to him. He almost always whispers back. When I have to walk him past Olive's room (when she's sleeping), I always whisper to him so that he whispers back. Otherwise, who knows what he might shout out as random neurons in his brain fire and make their way to his mouth muscle.
Does your LO understand the concept of being quiet? What are your tricks for keeping your LO quiet when needed?