AH-HA! I figured out how to evoke instant silence in a toddler!
Not by saying, “Shhh…” or “Be quiet!” or “Stop talking!”
The secret is to say, “Listen!”
The child’s natural response is to stop prattling and, well, LISTEN, which is a refreshingly quiet activity. Works like a charm when I have to sneak a spunky Lia down the hallway when Vivienne is still sleeping.