What difference does it make to the novel that it's narrated from a child's perspective? How would the book be different if an adult perspective was dominant?

Scout has an innate sense of equality and goodness. Her sense of innocence is combined with a scrappy sense of social justice that, in her way, reflects her father's sense of social justice. Scout is also a relatable character for the reader. Her childhood and nostalgic narrative of her past is witty and relatable. It is also important to note that Scout narrates her story as an adult. She is able to look back on her experience with the hindsight that maturity brings. I this sense we enjoy not only her childlike innocence but also a point of view that comes with the maturity and sober reflection. A different narrator would have significantly altered the mood and tone of the story.