Melanie Klein's object relations theory is built on careful observations of young children. The emphasis of Freud is on the first four to six years of life, contrasting the accentuation of Klein of the first four to six months of life.
Klein insists the drives of infants, such as hunger or sex, are directed to an object, such as a vagina, a penis, or a breast. The child's relation to the breast, according to Klein, is fundamental, serving as a prototype of relations to whole objects later in life, such as a father and mother.
The infantile tendency of relating to partial objects gives their experiences a fantasylike or unrealistic nature, affecting interpersonal relations later in life. Hence the tendency of Klein's ideas to shift the focus of psychoanalytic theory to the role early fantasy plays in the formation of interpersonal relationships from organically based stages of development.
Klein isn't the only theorist to speculate the importance of the early relationship between child and mother. The belief of Margaret Mahler is that the sense of identity of children is dependent on a three-step relationship with their mothers. The initial step is for the mother to cater to the basic needs of the infant and develop a symbiotic and safe relationship with the powerful mother. Finally, infants will establish their own identities and individuality upon emerging from the protective circles of their mothers.
The theory of Heinz Kohut is that the sense of self develops during infancy, when they are treated as unique people by their parents and others. John Bowlby also investigates the negative affects separation from the mother can pose on an infant. Finally, Mary Ainsworth, along with her colleagues, developed a method of measuring the type of attachment style infants display toward their caregivers.