A simple and easy-to-follow, interesting plot: children have short attention spans so a short, interesting story will keep their attention.
Likable and identifiable central characters: if a child likes a character, they will like the story.
A clear distinction between good and bad: books are important learningsources for children, having clear characters will help with the concept of "good" and "bad"
Interesting and engaging language: the book must be interesting so the kid will keep an interest.
Captivating and high-quality illustrations: children can get bored if its just words on a page. Illustrations can make children excited to read the book.
A teachable lesson: children are growing and learning and books can help provide a valuable lesson (life, friendship, love, diversity).
Relatable to a wide range of children: showing diversity in characters can help teach the lesson of acceptance to other races and religions.
Interesting setting that is either familiar or fantastic: children have short attention so a good setting will keep attentions.
A clear beginning, middle, and end: kids identify with a clear structure. Having a good structure means kids won't get lost in the story, which can make them frustration and make them give up on the book.