Step 1: Understanding the Concept:
The question asks about the primary focus of Katherine Mansfield's short story, 'Sun and Moon'.
Step 2: Detailed Explanation:
The story is told from the perspective of its two young protagonists, a little boy named Sun and his younger sister, Moon.
The entire narrative revolves around their experiences and perceptions during a party hosted by their parents.
Mansfield masterfully captures their sense of wonder, confusion, excitement, and eventual disappointment. The story delves into the innocent and often overlooked emotional world of young children as they navigate the confusing realm of adults.
Step 3: Final Answer:
In 'Sun and Moon', Mansfield beautifully portrays the subtle feelings of children.