keep quiet

Also, keep still.

Also, be quiet or still. Remain silent; same as hold one's tongue. For example, Please keep quiet about the party. Also see keep one's mouth shut.

Refrain from moving, stay in the same position; same as hold still. For example, The doctor gave the young boy a toy to keep him quiet while on the examining table, or It's hard for the baby to keep still unless he's sleeping. [Late 1300s]