Why did Ben Franklin know what was happening

Ben Franklin knew what was going on because he could tell by the way his mother reacted..... he could read her apprehension.

Ben looked up at him, his brown eyes troubled. When he spoke, his voice was intentionally low. "This is an evacuation, isn't it, Dad?"

"Yes." It was Mark's policy never to utter an untruth when replying to a question from the children.

"I knew it as soon as I got home from school. Usually Mother gets all excited and happy about traveling. Not today. She hated to pack. So I knew it."