What Makes a Children’s Book Cover Stand Out?

Comparing various children's books, I have seen how the design varies depending on the child's age and the type of story. In the case of picture books, for example, there might be much meaning in the facial expressions and colors, whereas in the chapter books, typography and mood play important roles. Considering childrens book covers specifically, I also pay attention to such aspects as the legibility of the title and whether or not the illustration provides sufficient context for the book without retelling the entire story.