John Bowlby & Mary Ainsworth, Attachment Theory in a paper by INGE BRETHERTON.
"It is not surprising that during infancy and early childhood these functions are either not operating at all or are doing so most imperfectly. During this phase of life, the child is therefore dependent on his mother performing them for him. She orients him in space and time, provides his environment, permits the satisfaction of some impulses, restricts others. She is his ego and his super-ego. Gradually he learns these arts himself, and as he does, the skilled parent transfers the roles to him. This is a slow, subtle and continuous process, beginning when he first learns to walk and feed himself, and not ending completely until maturity is reached. . . . Ego and super-ego development are thus inextricably hound up with the child’s primary human relationships. (Bowlby, 1951, p. 53)"