This would make a great procedure (Harry Wong). Count to five or hold up one finger at a time when the class needs to refocus. Discuss what occurs for each number at the beginning of the school year and eventually the reaction will be automatic.
OKAY short of telepathy this is the best way to talk to babies. We taught my younger brother sign language when he was a baby. We still use some of the signs, usually water and potty, especially in public.