Normal Growth and Development: Infancy

An infant is a baby who is 1 month to 1 year old. Most infants will learn to walk, talk, eat, and interact with others within the same general time frame. This is called normal growth and development.

Infants grow faster while he is in infancy than at any other time in his life. Caregivers will keep a record of his growth. They will write down the following changes each time you bring him in for a checkup:

• Weight: Infants double their birth weight by the time they are 6 months old. They will triple their birth weight by the time they're 1 year old. They will gain about 1 to 2 pounds per month. They will weigh close to 22 pounds by 1 year old. By 2 months, infants may look chubby. Their muscles will get stronger the more they learn to use his legs and arms.
• Length: Infants grow about 1 inch per month for the first 6 months of life. They will grow 1/2 inch per month between 6 months and 1 year of age. They should be 2 times longer than their birth length by the time they are 10 to 12 months old. Most of their growth happen in their trunk (mid section).

Jean Piaget's Cognitive Development Theory

Jean Piaget’s prominent work is his Theory on the four stages of cognitive development. 

He was one of the most influential researchers in the area of developmental psychology in the 20th century whose primary interest was in biological influences on how we come to know, and the developmental stages we move through as we acquire this ability (Singer & Revenson, 1997).

Piaget (1973) believed that the child plays an active role in the growth of intelligence and learns by doing. He regarded the child as a philosopher who perceives the world only as he has experienced it. 

Therefore, most of Piaget’s inspiration in cognitive and intellectual development came from observations of children. In fact, Piaget observed and studied his own three children through each stage of their cognitive development.

The Theory of Cognitive Development focuses on mental processes such as perceiving, remembering, believing, and reasoning. Reasoning is the essence of intelligence, and reasoning is what Piaget studied in order to discover “how we come to know” (Singer & Revenson, 1997). Piaget believed that cognitive development is cumulative; that is, understanding a new experience grows out of a previous learning experience.

Erick Erikson's Theory of Psychosocial Development

Erik Erikson's theory of psychosocial development is one of the best-known theories of personality. Much like Sigmund Freud, Erikson believed that personality develops in a series of stages. Unlike Freud's theory of psychosexual stages, Erikson's theory describes the impact of social experience across the whole lifespan.

One of the main elements of Erikson's psychosocial stage theory is the development of ego identity. Ego identity is the conscious sense of self that we develop through social interaction. According to Erikson, our ego identity is constantly changing due to new experiences and information we acquire in our daily interactions with others.


Identity refers to all of the beliefs, ideals, and values that help shape and guide a person's behavior. The formation of identity is something that begins in childhood and becomes particularly important during adolescence, but it is a process that continues throughout life. Our personal identity gives each of us an integrated and cohesive sense of self that endures and continues to grow as we age.