a man who helps children to cross the road near a school by standing in the middle of the road and holding up a stick with a round sign on it that means that the traffic must stop

Wait for the lollipop man to stop the traffic and help you across the road.

A shortage of lollipop men and women is putting children in increased danger on their way to school. 安全指挥员的短缺使孩子们在上学的路上面临更多的危险。