The stages of cognitive development in children were studied and defined by a psychologist named Jean Piaget. He coined the term cognitive development, and classified four stages throughout childhood where the way in which we learn and understand the world is known to shift. Here is a look at Piaget's four stages of cognitive development:
Sensorimotor
This is the earliest way we learn. It begins at birth, and continues to about eighteen months. Learning at this stage is all about the five senses- what does the world look, sound, feel, taste, and smell like? Much of the world is explored through the mouth at this stage, because it covers three bases at once- touch, taste, and smell. One of the most important milestones in this stage is object permanence- the idea that something still exists even if you don't see it. This is a clue that memory is developing. One of the earliest versions of this is watching a child drop something, and look for where it went. Once they understand to look for it, then object permanence has been achieved.
Perioperational
This stage goes from toddlerhood through about age 7. Children in this stage understand how to think in symbols, and because of this they can learn letters and numbers and understand that they stand for something else. They begin understanding cause and effect, (If I push Sally, then I will have to sit in the time-out chair) though the reason behind that cause and effect may still be above them.
Concrete Operational
As they reach this stage, they will begin to understand that their feelings about something may be unique to them, and that others may have different points of view. They cease to be the center of the universe in their minds. This is the beginning of abstract thought, and develops between age 7 and early adolescence. Logic here begins to come into play in the form of comparisons- they understand timelines, and bigger vs smaller. Money and earning enough to afford something, consequences for actions, and other black and white concepts begin to show up. Near the end of this stage they will begin to question the gray in these situations, leading to the final stage of development.
Formal Operational
This is the last stage of cognitive development and goes from adolescence to adulthood. Many will argue that those who engage in regular learning never have an end to this stage, but continue to develop until the end of their life. Concepts like fairness and justice come into play, and later they can combine symbols and logic to begin doing things like algebraic equations. Hypothetical situations can be discussed, even when the needs of an individual person are completely removed from the equation.