Learning Child Behavioral Psychology

Why does the child cry? What needs do general children cry? Is it only means that cry implies children feel unhappy or children have emotion problem? Does child cry represent the child hopes to do something, but the child feels difficult to do? Is child feels need to cry, his /her crying behavior may she / she learns easily after he /she crys? Can cry assist child learns more easily?
In my this book, I shall attempt to explain whether what childs wants when the child drys. Parents and teachers may learn whether the child crys, the child hopes what he / she feels need in order to improve learn ability or learning attitude more better in possible.