It's hard to believe, but only 100 years ago, children were considered little more than empty vessels, unworthy of individual respect or close examination. In the early 20th century, however, researchers in the fields of biology and psychology began to study early childhood development and the impact of a child's environment on her overall well-being. Several early theories of childhood development continue to influence educators and psychologists today.
Viennese doctor Sigmund Freud believed that children develop psychologically based on how their parents react to their early childhood experiences with toilet training, aggression and sexuality. His "psychosexual" theory proposed that children progress through several distinct stages on their way to adulthood: Oral, Anal, Phallic, Latency and Genital. Experiences with sexual gratification or pleasure experienced from a particular part of the body during any of the developmental phases, or interruption of a phase by trauma, can lead to neurosis. The theory also introduces the notion of a subconscious "id," which seeks gratification at all costs, and a dominating "ego," the reasonable mind that assumes control of one's personality. A "superego" also exists, internalizing parental and authoritarian rules for living and providing guidance for the ego and frustration for the id.
Influenced by Freud's work, psychologist Erik Erikson's theory of early childhood behavior was based on the progressive development of a person's cognitive sense of self. In his opinion, children form their worldview and sense of identity based upon their experiences during several stages: Trust vs. Mistrust (birth to 18 months), Autonomy vs. Shame or Doubt (18 months to 3 years), Initiative vs. Guilt (3 to 5 years), Industry vs. Inferiority (5 to 12 years) and later cognitive developments. How effectively children are stimulated during the various early stages of development, thought Erikson, determines how well-adjusted and productive they become as adults.
Scholar and psychologist Lawrence Kohlberg's theory of psychology proposed three distinct and linear levels of moral development, divided into two stages each. The first level, which occurs during early childhood (before the teen years), he called the Preconventional, consequence-driven level, and is characterized by two stages: Obedience and Punishment, where absolute rules are always followed by consequences; and Individualism and Exchange, where self-interest determines which rules can be negotiated.
Swiss developmental psychologist Jean Piaget theorized that all children develop linearly through four stages: the Sensorimotor stage (birth to 2 years old), Preoperational stage (2 to 7 years), Concrete Operations stage (7 to 11 years), and Formal Operations stage (past 11). During the Sensorimotor stage, the child assimilates knowledge about her environment and learns to differentiate between herself and the world. She learns to accommodate for unexpected objects and outcomes, and classifies objects according to their basic features during the Preoperational stage. In the Concrete Operations stage, she develops the ability to think abstractly and to conceptualize ideas to explain her own experiences.
Developmental psychologist Urie Bronfenbrenner first proposed the Ecological Systems Theory, which is also called the Bioecological Systems Theory or Human Ecology Theory. The main premise of this theory is that a child's development is influenced by five environmental systems: the Microsystem, which entails all social interactions with those who are closest to the child; the Mesosystem, those interactions between the members of the child's microsystem; the Exosystem, the link between a child's direct environmental context and the greater social context; the Macrosystem, the cultural context of a child; and the Chronosystem, or changes that occur over the lifespan of an individual.