This article is the second in a series concerned with child development. The goals of this series are to discuss what is known about how children develop from birth through adolescence, and to offer tips on how to use this developmental knowledge to improve parenting skills. This particular document will survey what is known about how children develop between birth and age 24 months, a period known as infancy.
Children develop in many different ways at the same time. Different aspects of children's development are never at rest or waiting for other parts to catch up. Instead, development is simultaneous. While physical growth and maturity are the most obvious signs that development is occurring, children also develop cognitively (mentally), socially, emotionally, and sexually. This document is organized so that each type of development is described separately and nothing important is left out.
The milestones of development are discussed in terms of easy to understand measurements such as weight, height, or the presence or absence of reflexes. However, not all important aspects of development can be easily measured. Mental and emotional development are difficult to measure directly. This article describes the best available theories to understand what is occurring inside each child's head.
The works of five theorists work are considered in the course of this series: Freud, Erikson, Kohlberg, Piaget, and Bronfenbrenner. Among these theorists, the works of Piaget and Erikson speak most directly to the infancy period of life covered here. Infancy corresponds to Piaget's "Sensorimotor" stage of cognitive development, and to two of Erikson's stages; the "trust vs. mistrust" stage during the first year of life, and the "autonomy vs. shame and doubt" stage that follows closely after. Piaget's work describes how infants come to understand their world through their bodies and senses. Erikson's work describes how children develop an appreciation of both their individuality and simultaneous dependency on others, and how children's attitudes towards themselves and others are influenced by their experiences and by the type of support and nurturing they receive.
Development is often described by referring to particular developmental milestones that are significant achievements of one sort or another such as crawling, walking, or first words. Developmental milestones are presented as occurring at particular ages. Even though developmental milestones do commonly occur at particular ages, children develop at their own pace. Some children will reach a given milestone early, while others will reach it later on. All of this is perfectly normal.