Development is often divided into specific domains, such as gross motor, fine motor, language, cognition, and social/emotional growth. These designations are useful, but substantial overlap exists. Studies have established average ages at which specific milestones are reached, as well as ranges of normality. In a normal child, progress within the different domains varies, as in the toddler who walks late but speaks in sentences early (see Table: Developmental Milestones*).
Environmental influences, ranging from nutrition to stimulation and from the impact of disease to the effects of psychologic factors, interact with genetic factors to determine the pace and pattern of development.
Assessment of development occurs constantly as parents, school personnel, and clinicians evaluate children. Many tools are available for monitoring development more specifically. The Denver Developmental Screening Test II facilitates evaluation in several domains. The scoring sheet indicates the average ages for achieving certain milestones and nicely shows the critical concept of a range of normality. Other tools can also be used (see Table: Developmental Milestones*).
Motor development includes fine motor (eg, picking up small objects, drawing) and gross motor (eg, walking, climbing stairs) skills. It is a continuous process that depends on familial patterns, environmental factors (eg, when activity is limited by prolonged illness), and specific disorders (eg, cerebral palsy, intellectual disability, muscular dystrophy). Children typically begin to walk at 12 months, can climb stairs holding on at 18 months, and run well at 2 years, but the age at which these milestones are achieved by normal children varies widely. Motor development cannot be significantly accelerated by applying increased stimulation.
The ability to understand language precedes the ability to speak; children with few words usually can understand a great deal. Although delays in expressive speech are typically not accompanied by other developmental delays, all children with excessive language delays should be evaluated for the presence of other delays in development. Children who have delays in both receptive and expressive speech more often have additional developmental problems. Evaluation of any delay should start with an assessment of hearing. Most children who experience speech delay have normal intelligence. In contrast, children with accelerated speech development are often of above-average intelligence.
Speech progresses from the utterance of vowel sounds (cooing) to the introduction of syllables that start with consonants (ba-ba-ba). Most children can say “Dada” and “Mama” specifically by 12 months, use several words by 18 months, and form 2- or 3-word phrases by 2 years. The average 3-year-old child can carry on a conversation. A 4-year-old child can tell simple stories and can engage in conversation with adults or other children. A 5-year-old child may have a vocabulary of several thousand words.
Even before age 18 months, children can listen to and understand a story being read to them. By age 5, children are able to recite the alphabet and to recognize simple words in print. These skills are all fundamental to learning how to read simple words, phrases, and sentences. Depending on exposure to books and natural abilities, most children begin to read by age 6 or 7. These milestones are highly variable.
Cognitive development refers to the intellectual maturation of children. Increasingly, appropriate attachments and nurturing in infancy and early childhood are recognized as critical factors in cognitive growth and emotional health. For example, reading to children from an early age, providing intellectually stimulating experiences, and providing warm and nurturing relationships all have a major impact on growth in these domains.
Intellect is appraised in young children by observations of language skills, curiosity, and problem-solving abilities. As children become more verbal, intellectual functioning becomes easier to assess using a number of specialized clinical tools. Once children start school, they undergo constant monitoring as part of the academic process.
At age 2 years, most children understand the concept of time in broad terms. Many 2- and 3-year-old children believe that anything that happened in the past happened "yesterday," and anything that will happen in the future will happen "tomorrow." A child at this age has a vivid imagination but has difficulty distinguishing fantasy from reality.
By age 4 years, most children have a more complicated understanding of time. They realize that the day is divided into morning, afternoon, and night. They can even appreciate the change in seasons.
By age 7 years, children's intellectual capabilities become more complex. By this time, children become increasingly able to focus on more than one aspect of an event or situation at the same time. For example, school-aged children can appreciate that a tall, slender container can hold the same amount of water as a short, broad one. They can appreciate that medicine can taste bad but can make them feel better, or that their mother can be angry at them but can still love them. Children are increasingly able to understand another person's perspective and so learn the essentials of taking turns in games or conversations. In addition, school-aged children are able to follow agreed-upon rules of games. Children of this age are also increasingly able to reason using the powers of observation and multiple points of view.
Emotion and behavior are based on the child's developmental stage and temperament. Every child has an individual temperament, or mood. Some children may be cheerful and adaptable and easily develop regular routines of sleeping, waking, eating, and other daily activities. These children tend to respond positively to new situations. Other children are not very adaptable and may have great irregularities in their routine. These children tend to respond negatively to new situations. Still other children are in between.
Emotional growth and the acquisition of social skills are assessed by watching children interact with others in everyday situations. When children acquire speech, the understanding of their emotional state becomes much more accurate. As with intellect, emotional functioning can be delineated more precisely with specialized tools.
Crying is infants' primary means of communication. Infants cry because they are hungry, uncomfortable, distressed, and for many other reasons that may not be obvious. Infants cry most—typically 3 hours/day—at age 6 weeks, usually decreasing to 1 hour/day by age 3 months. Parents typically offer crying infants food, change their diaper, and look for a source of pain or discomfort. If these measures do not work, holding or walking with the infant sometimes helps. Occasionally nothing works. Parents should not force food on crying infants, who will readily eat if hunger is the cause of their distress.
At about age 8 months, infants normally become more anxious about being separated from their parents. Separations at bedtime and at places like child care centers may be difficult and can be marked by temper tantrums. This behavior can last for many months. For many older children, a special blanket or stuffed animal serves at this time as a transitional object that acts as a symbol for the absent parent.
At age 2 to 3 years, children begin to test their limits and do what they have been forbidden to do, simply to see what will happen. The frequent "nos" that children hear from parents reflect the struggle for independence at this age. Although distressing to parents and children, tantrums are normal because they help children express their frustration during a time when they cannot verbalize their feelings well. Parents can help decrease the number of tantrums by not letting their children become overtired or unduly frustrated and by knowing their children's behavior patterns and avoiding situations that are likely to induce tantrums. Some young children have particular difficulty controlling their impulses and need their parents to set stricter limits around which there can be some safety and regularity in their world.
At age 18 months to 2 years, children typically begin to establish gender identity. During the preschool years, children also acquire a notion of gender role, of what boys and girls typically do. Exploration of the genitals is expected at this age and signals that children are beginning to make a connection between gender and body image.
Between age 2 years and 3 years, children begin to play more interactively with other children. Although they may still be possessive about toys, they may begin to share and even take turns in play. Asserting ownership of toys by saying, "That is mine!" helps establish the sense of self. Although children at this age strive for independence, they still need their parents nearby for security and support. For example, they may walk away from their parents when they feel curious only to later hide behind their parents when they are fearful.
At age 3 to 5 years, many children become interested in fantasy play and imaginary friends. Fantasy play allows children to safely act out different roles and strong feelings in acceptable ways. Fantasy play also helps children grow socially. They learn to resolve conflicts with parents or other children in ways that help them vent frustrations and maintain self-esteem. Also at this time, typical childhood fears like that of "the monster in the closet" emerge. These fears are normal.
At age 7 to 12 years, children work through numerous issues: self-concept, the foundation for which is laid by competency in the classroom; relationships with peers, which are determined by the ability to socialize and fit in well; and family relationships, which are determined in part by the approval children gain from parents and siblings. Although many children seem to place a high value on the peer group, they still look primarily to parents for support and guidance. Siblings can serve as role models and as valuable supports and critics regarding what can and cannot be done. This period of time is very active for children, who engage in many activities and are eager to explore new activities. At this age, children are eager learners and often respond well to advice about safety, healthy lifestyles, and avoidance of high-risk behaviors.