"You have a bag of sand, a long knife and a cudgel."
"What's a cudgel?" said the 6-year-old.
"Like a stick," said her big brother, who is 15 years old. He and three of his sisters were sitting in a circle in the living room, their faces grave and intent. Outside, the sun shone on a sparkling September afternoon, but the children wanted to be indoors, where they could concentrate.
"Why do I need...