What method do the children use to communicate with Mr. Benedict?

The children utilize Morse Code as their method of communication with Mr. Benedict throughout their adventures. This choice highlights the cleverness and resourcefulness of the group, as they use a coded form of communication that is not easily understood by those around them, thereby allowing them to convey important messages discreetly. Morse Code provides a sense of secrecy and creativity, fitting the overall theme of intelligence and problem-solving that permeates the story. The use of this method underscores the children's ingenuity and reinforces their commitment to working together in a clever manner to navigate the challenges they face.

Other methods like written letters or direct verbal communication would not offer the same level of discretion, and sign language, while effective, does not feature prominently in the interactions depicted in the book. Morse Code thus stands out as a more strategic choice for their secretive communications with Mr. Benedict.