Developmental psychology
Kohlberg’s Moral Development Theory:
Kohlberg’sMoral judgment data from a longitudinal study of 26 undergraduates are scored by Kohlberg’s newly revised manual and replicate his original finding that a significant percentage of subjects appear to regress from adolescence to adulthood. The persistence of relativistic regression in these data suggests the need to revise the theory. The same hypothetical moral dilemmas are also scored according to an alternative coding scheme based on the hypothesis of an adult form of cognitive development. Results indicate that the Kohlberg regressors are progressors when evaluated against a standard of commitment in relativism instead of absolute principles of justice. Real-life data on the same subjects suggest that this progression is related to actual experiences of moral conflict and choice which lead to the restructuring of moral judgment to a more dialectical mode. It is suggested that this alternative notion of postconventional development is necessary for understanding (and scoring) adult moral judgment.
Piaget's theory of cognitive development:
Piaget's theory of cognitive development is a comprehensive theory about the nature and development of human intelligence, first developed by Jean Piaget. It is primarily known as a developmental stage theory, but in fact, it deals with the nature of knowledge itself and how humans come gradually to acquire, construct, and use it. To Piaget, cognitive development was a progressive reorganization of mental processes as a result of biological maturation and environmental experience. Children construct an understanding of the world around them, then experience discrepancies between what they already know and what they discover in their environment.[1] Moreover, Piaget claims the idea that cognitive development is at the center of human organism and language is contingent on cognitive development. Below, there is first a short description of Piaget's views about the nature of intelligence and then a description of the stages through which it develops until maturity
Freud's Stages of Psychosexual Development:
Freud's theory of psychosexual development is one of the best known, but also one of the most controversial. Freud believed that personality develops through a series of childhood stages during which the pleasure-seeking energies of the become focused on certain erogenous areas. This psychosexual energy was described as the driving force behind behavior.
If these psychosexual stages are completed successfully, the result is a healthy personality. If certain issues are not resolved at the appropriate stage, can occur. A fixation is a persistent focus on an earlier psychosexual stage. Until this conflict is resolved, the individual will remain "stuck" in this stage. For example, a person who is fixated at the oral stage may be over-dependent on others and may seek oral stimulation through smoking, drinking, or eating.

Erikson's Theory of Psychosocial Development:
Erik Erikson's theory of psychosocial development is one of the best-known theories of personality in psychology. 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. In addition to ego identity, Erikson also believed that a sense of competence motivates behaviors and actions. Each stage in Erikson's theory is concerned with becoming competent in an area of life. If the stage is handled well, the person will feel a sense of mastery, which is sometimes referred to as ego strength or ego quality.If the stage is managed poorly, the person will emerge with a sense of inadequacy.
Language development theory: It is a process starting early in human life. Infants start without language, yet by 4 months of age, babies can discriminate speech sounds and engage in babbling. Some research has shown that the earliest learning begins in utero when the fetus starts to recognize the sounds and speech patterns of its mother's voice.
Usually, productive language is considered to begin with a stage of preverbal communication in which infants use gestures and vocalizations to make their intents known to others. According to a general principle of development, new forms then take over old functions, so that children learn words to express the same communicative functions which they had already expressed by preverbal means. Language development is thought to proceed by ordinary processes of learning in which children acquire the forms, meanings and uses of words and utterances from the linguistic input. The method in which we develop language skills is universal[1] however, the major debate is how the rules of syntax are acquired. There are two major approaches to syntactic development, an empiricist account by which children learn all syntactic rules from the linguistic input, and a nativist approach by which some principles of syntax are innate and are transmitted through the human genome.
The nativist theory, proposed by Noam Chomsky, argues that language is a unique human accomplishment. He argues that linguistic input from the environment is limited and full of errors. Therefore, nativists assume that it is impossible for children to learn linguistic information solely from their environment. However, because children possess this LAD, they are in fact, able to learn language despite incomplete information from their environment.