Stand next to the kid getting laughed at. You don’t have to say anything. Where you stand is loud.

Position speaks before words do. When someone is being made small, the people nearby are all making a choice, including the ones who think they are neutral. Moving to stand beside that person changes the arithmetic of the room without requiring a speech or a confrontation.

You do not need the perfect line. Walking over, sitting down, asking an ordinary question about something else entirely is often enough to break the moment. If that feels like a lot, start by not laughing.