ANSWER: The brain's nerve cells are sculpted by heredity and experience. As a child's brain develops, neural connections grow more numerous and complex. Experiences then trigger a pruning process, in which unused connections weaken and heavily used ones strengthen. This process continues until puberty. Early childhood is an important period for shaping the brain, but our brain modifies itself in response to our learning throughout life. In childhood, complex motor skills—sitting, standing, walking—develop in a predictable sequence, though the timing of that sequence is a function of individual maturation and culture. We have no conscious memories of events occurring before about age 3½. This infantile amnesia occurs in part because major brain areas have not yet matured.

ANSWER: In his theory of cognitive development, Jean Piaget proposed that children actively construct and modify their understanding of the world through the processes of assimilation and accommodation. They form schemas that help them organize their experiences. Progressing from the simplicity of the sensorimotor stage of the first two years, in which they develop object permanence, children move to more complex ways of thinking. In the preoperational stage (about age 2 to about 6 or 7), they develop a theory of mind. In the preoperational stage, children are egocentric and unable to perform simple logical operations. At about age 7, they enter the concrete operational stage and are able to comprehend the principle of conservation. By about age 12, children enter the formal operational stage and can reason systematically. Research supports the sequence Piaget proposed, but it also shows that young children are more capable, and their development more continuous, than he believed. Lev Vygotsky's studies of child development focused on the ways a child's mind grows by interacting with the social environment. In his view, parents and caretakers provide temporary scaffolds enabling children to step to higher levels of learning.

ANSWER: Autism spectrum disorder (ASD) is a disorder marked by social deficiencies and repetitive behaviors. By age 8, 1 in 68 U.S. children now gets diagnosed with ASD, though the reported rates vary by place. The increase in ASD diagnoses has been offset by a decrease in the number of children with a “cognitive disability” or “learning disability,” suggesting a relabeling of children's disorders.

ANSWER: At about 8 months, soon after object permanence develops, children separated from their caregivers display stranger anxiety. Infants form attachments not simply because parents gratify biological needs but, more important, because they are comfortable, familiar, and responsive. Many birds and other animals have a more rigid attachment process, called imprinting, that occurs during a critical period.

ANSWER: Attachment has been studied in strange situation experiments, which show that some children are securely attached and others are insecurely attached. Infants' differing attachment styles reflect both their individual temperament and the responsiveness of their parents and child-care providers. Adult relationships seem to reflect the attachment styles of early childhood, lending support to Erik Erikson's idea that basic trust is formed in infancy by our experiences with responsive caregivers.

ANSWER: Children are very resilient, but those who are severely neglected by their parents, or otherwise prevented from forming attachments at an early age, may be at risk for attachment problems.

ANSWER: Parenting styles—authoritarian, permissive, and authoritative—reflect varying degrees of control. Children with high self-esteem tend to have authoritative parents and to be self-reliant and socially competent, but the direction of cause and effect in this relationship is not clear. Child-raising practices reflect both individual and cultural values.

ANSWER: We have no conscious memories of events occurring before about age 3½, in part because major brain areas have not yet matured.

ANSWER: Infants in Piaget's sensorimotor stage tend to be focused only on their own perceptions of the world and may, for example, be unaware that objects continue to exist when unseen. A child in the preoperational stage is still egocentric and incapable of appreciating simple logic, such as the reversibility of operations. A preteen in the concrete operational stage is beginning to think logically about concrete events but not about abstract concepts.

ANSWER: Before these studies, many psychologists believed that infants became attached to those who nourished them.