By the beginning of middle childhood, children typically have acquired a leaner, more athletic appearance. Girls and boys still have similar body shapes and proportions until both sexes reach puberty, the process whereby children sexually mature into teenagers and adults. After puberty, secondary sexual characteristics—breasts and curves in females, deeper voice and broad shoulders in males—make distinguishing females from males much easier.
Girls and boys grow about 2 to 3 inches and gain about 7 pounds per year until puberty. Skeletal bones and muscles broaden and lengthen, which may cause children (and adolescents) to experience growing pains. Skeletal growth in middle childhood is also associated with losing the deciduous teeth, or baby teeth.
Throughout most of middle childhood, girls are smaller than boys and have less muscle mass. As girls enter puberty, however, they may be considerably larger than boys of the same age, who enter puberty a few years later. Once boys begin sexually maturing, their heights and weights eventually surpass the heights and weights of girls of the same age.
Brain and nervous system development
Brain and nervous system developments continue during middle childhood. More complex behavioral and cognitive abilities become possible as the central nervous system matures.
Early in middle childhood, a growth spurt occurs in the brain so that by age 8 or 9, the organ is nearly adult‐size. Brain development during middle childhood is characterized by growth of specific structures, especially the frontal lobes. These lobes, located in the front of the brain just under the skull, are responsible for planning, reasoning, social judgment, and ethical decision making, among other functions. Damage to this part of brain results in erratic emotional outbursts, inability to plan, and poor judgment. The most anterior (front) portion of the frontal lobes is the prefontal cortex, which appears to be responsible for personality.
As the size of the frontal lobes increases, children are able to engage in increasingly difficult cognitive tasks, such as performing a series of tasks in a reasonable order. An example is assembling a mechanical toy: unpacking the pieces, connecting the parts, making the model move by adding a power source—a series of tasks that must be completed in the correct order to achieve certain results.
Lateralization of the two hemispheres of the brain, also continues during middle childhood, as does maturation of the corpus callosum (the bands of neural fibers connecting the two cerebral hemispheres), and other areas of the nervous system. Interestingly, children achieve concrete operations around age 7 when the brain and nervous systems have developed a certain amount of neural connections. When these neural connections have developed, a child's ability to perceive and think about the world advances from an egocentric, magical viewpoint to a more concrete and systematic way of thinking.
Motor skills
Motor skills are behavioral abilities or capacities. Gross motor skills involve the use of large bodily movements, and fine motor skills involve the use of small bodily movements. Both gross and fine motor skills continue to refine during middle childhood.
Children love to run, jump, leap, throw, catch, climb, and balance. Children play baseball, ride bikes, roller skate, take karate lessons, take ballet lessons, and participate in gymnastics. As school‐age children grow physically, they become faster, stronger, and better coordinated. Consequently, during middle childhood, children become more adept at gross motor activities.
Children enjoy using their hands in detailed ways, too. From early in preschool, children learn and practice fine motor skills. Preschool children cut, paste, mold, shape, draw, paint, create, and write. These children also learn such skills as tying shoelaces, untying knots, and flossing their teeth. Some fortunate children are able to take music lessons for piano, violin, flute, or other instruments. Learning to play an instrument helps children to further develop their fine motor skills. In short, along with the physical growth of children comes the development of fine motor skills, including the sense of competence and confidence to use these skills.
Health
Middle childhood tends to be a very healthy period of life in Western societies. The typical minor illnesses of early childhood—colds, coughs, and stomachaches—are likely to lessen in frequency in middle childhood. This improved resistance to common illnesses is probably due to a combination of increased immunity from previous exposures and improved hygiene and nutritional practices. Minor illnesses occur, but most illnesses do not require medical attention. Minor illnesses may help children learn psychological coping skills and strategies for dealing with physical discomforts.
Major illnesses for school‐age children are the same as major illnesses for younger children: influenza, pneumonia, cancer, human immunodeficiency virus (HIV), and acquired immunodeficiency syndrome (AIDS). But obesity, or being 20 percent or more above one's ideal weight, is a special health problem that occurs during the school years. About 25 percent of school‐age children in the United States today are obese, and the majority of these children go on to become obese adults. Obesity in adulthood is related to heart problems, high blood pressure, and diabetes. Although obese children are not at the same medical risks as obese adults, these children should master effective eating and exercise habits as early as possible to decrease the risk of later obesity‐ and health‐related problems.
The majority of disabilities and deaths in middle childhood are the result of injuries from accidents. In the United States, nearly 22 million children are hurt in accidents each year. For children, the most common deadly accidents result from being struck by moving vehicles. Accidents may occur at, near, and away from home; therefore, adequate adult supervision is always important. Injuries occurring at school are usually the result of playground‐ and sports‐related accidents. Consequently, children should always wear protective headgear and other safety gear when playing sports and riding bikes. Other causes of death in middle childhood include cancer, congenital defects, homicide, and deadly infections.