The concept of childhood is relatively new; in most medieval societies, childhood did not exist. At approximately seven years of age, children were considered little adults with similar expectations for a job, marriage, and legal consequences. Charles Darwin originated ideas of childhood development in his work on the origins of ethology (the scientific study of the evolutionary basis of behavior) and "A Biographical Sketch of an Infant," first published in 1877.
It wasn't until the 20th century that developmental theories emerged. When conceptualizing cognitive development, we cannot ignore the work of Jean Piaget. Piaget suggested that when young infants experience an event, they process new information by balancing assimilation and accommodation. Assimilation is taking in new information and fitting it into previously understood mental schemas. Accommodation is adapting and revising a previously understood mental schema according to the novel information. Piaget divided child development into four stages.
The first stage, Sensorimotor (ages 0 to 2 years of age), is the time when children master two phenomena: causality and object permanence. Infants and toddlers use their sense and motor abilities to manipulate their surroundings and learn about the environment. They understand a cause-and-effect relationship, like shaking a rattle may produce sound and may repeat it or how crying can make the parent(s) rush to give them attention. As the frontal lobe matures and memory develops, children in this age group can imagine what may happen without physically causing an effect; this is the emergence of thought and allows for the planning of actions. Object permanence emerges around six months of age. It is the concept that objects continue to exist even when they are not presently visible.
Second is the "Pre-operational" stage (ages 2 to 7 years), when a child can use mental representations such as symbolic thought and language. Children in this age group learn to imitate and pretend to play. This stage is characterized by egocentrism, i.e., being unable to perceive that others can think differently than themselves, and everything (good or bad) somehow links to the self.
Third is the "Concrete Operational stage" (ages 7 to 11 years), when the child uses logical operations when solving problems, including mastery of conservation and inductive reasoning. Finally, the Formal Operational stage (age 12 years and older) suggests an adolescent can use logical operations with the ability to use abstractions. Adolescents can understand theories, hypothesize, and comprehend abstract ideas like love and justice.
Childhood cognitive development and the Piaget stages are poorly generalizable. For example, conservation may overlap between the Pre-operational and Concrete Operational stages as the child masters conservation in one task and not in another. Similarly, the current understanding is that a child masters the "Theory of Mind" by 4 to 5 years, much earlier than when Piaget suggested that egocentrism resolves.
Stages of Cognitive Development (Problem-Solving and Intelligence)
The word intelligence derives from the Latin "intelligere," meaning to understand or perceive. Problem-solving and cognitive development progress from establishing object permanence, causality, and symbolic thinking with concrete (hands-on) learning to abstract thinking and embedding of implicit (unconscious) to explicit memory development.
Birth to two months: The optical focal length is approximately 10 inches at birth. Infants actively seek stimuli, habituate to the familiar, and respond more vigorously to changing stimuli. The initial responses are more reflexive, like sucking and grasping. The infant can fix and follow a slow horizontal arc and eventually will follow past the midline. Contrasts, colors, and faces are preferred. The infant will distinguish familiar from moderately novel stimuli. As habituation to the faces of caregivers occurs, preferences are developed. The infant will stare momentarily where at the place from where an object has disappeared (lack of object permanence). At this stage, high-pitched voices are preferred.
Two to six months: Children in this age bracket engage in a purposeful sensory exploration of their bodies, staring at their hands and reaching and touching their body parts; this builds the concepts of cause and effect and self-understanding. Sensations and changes outside of themselves are appreciated with less regularity. As motor abilities are mastered, something that happens by chance will be repeated. For example, touching a button may light up the toy, or crying can cause the appearance of the caregiver. Routines are appreciated in this age group.
Six to twelve months: Object permanence emerges in this age group as the toddler looks for objects. A six-month-old will look for partially hidden objects, while a nine-month-old will look for wholly hidden objects and uncover them; this includes engaging in peek-a-boo-type games. Separation and stranger anxiety emerge as the toddler understands that out of sight is not out of mind. As motor abilities advance, sensory exploration of the environment occurs via reaching, inspecting, holding, mouthing, and dropping objects. They learn to manipulate their environment, learning cause and effect by trial and error, like banging two blocks together can produce a sound. Eventually, as Piaget suggested, mental schemas are built, and objects can be used functionally; for example, by intentionally pressing a button to open and reach inside a toy box.
Twelve to eighteen months: Around this time, motor abilities make it easier for the child to walk and reach, grasp, and release. Toys can be explored, made to work, and novel play skills emerge. Gestures and sounds can be imitated. Egocentric pretend play emerges. As object permanence and memory advance, objects can be found after witnessing a series of displacements, and moving objects can be tracked.
Eighteen months to two years: As memory and processing skills advance and frontal lobes mature, outcomes are imagined without so much physical manipulation, and new problem-solving strategies emerge without rehearsal. Thought arises, and there is the ability to plan actions. Object permanence is wholly established, and objects can be searched for by anticipating where they may be without witnessing their displacement. At 18 months, symbolic play expands from just the self; the child may attempt to feed a toy along with themselves, and housework may be imitated.
Two to five years: During this stage, the preschool years, magical and wishful thinking emerges; for example, the sun went home because it was tired. This ability may also give rise to apprehensions with fear of monsters, and having logical solutions may not be enough for reassurance. Perception will dominate over logic, and giving them an imaginary tool, like a monster spray, to help relieve that anxiety may be more helpful. Similarly, conservation and volume concept lacks, and what appears bigger or larger is more. For example, one cookie split into may equal two cookies.
Children in the preschool stage have a poor concept of cause and may think sickness is due to misbehavior. They are egocentric in their approach and may look at situations from only their point of view, offering comfort from a favorite stuffed toy to an upset loved one. At 36 months, a child can understand simple time concepts, identify shapes, compare two items, and count to three. Play becomes more comprehensive. At 48 months, children can count to four, identify four colors and understand opposites.
At five years of age, pre-literacy and numeracy skills further; five-year-old children can count to ten accurately, recites the alphabet by rote, and recognize a few letters. A child also develops hand preference at this age. Play stories become even more detailed between four and five years and may include imaginary scenarios, including imaginary friends. Playing with some game rules and obedience to those rules also establishes during the preschool years. Rules can be absolute.
Six to twelve years: During early school years, scientific reasoning and understanding of physical laws of conservation, including weight and volume, develop. A child can understand multiple points of view and can understand one perspective of a situation. They realize the rules of the game can change with mutual agreement. Basic literacy skills of reading and numbers are mastered initially. Eventually, around third to fourth grade, the emphasis shifts from learning to read to reading to learn and from spelling to composition writing. All these stages need mastery of sustained attention and processing skills, receptive and expressive language, and memory development and recall. The limitation of this stage is an inability to comprehend abstract ideas and reliance on logical answers.
Twelve years and older: During this age, adolescents can exercise logic systematically and scientifically. They can simultaneously apply abstract thinking to solve algebraic problems and multiple logics to reach a scientific solution. It is easier to use these concepts for schoolwork. Later in adolescence and early adulthood, these concepts can also apply to emotional and personal life problems. Magical thinking or following ideals guides decisions more than wisdom. Some may have more influence from religious or moral rules and absolute concepts of right and wrong. Questioning the prevalent code of conduct may cause anxiety or rebellion and eventually lead to the development of personal ethics. Side by side, social cognition, apart from self, also is developing, and concepts of justice, patriarchy, politics, etc. establish. During late teens and early adulthood, thinking about the future, including ideas such as love, commitment, and career goals, become important.