Final answer:
The children gathering stones signifies the literary device called foreshadowing, hinting at important future events in the story, and the correct option is 'B' foreshadowing.
Step-by-step explanation:
The literary device indicated by the description of children gathering stones into a pile at the exposition of a story is foreshadowing. Foreshadowing is a technique used by authors to give clues or hints about events that will happen later in the narrative.
The pile of stones, as presented, suggests that they will play a significant role as the story unfolds, creating anticipation or tension for the reader. This detail has been intentionally included to prepare the audience for subsequent developments, and it can be a particularly powerful way of adding depth and intrigue to a story.
Foreshadowing differs from metaphors and similes, which are comparisons, and from puns, which play on words. Thus, in the context provided, the correct option is B, foreshadowing.