During the preschool years from ages 2 to 6, children experience significant physical, motor, and cognitive development. Physically, children nearly double in height and weight during this time. Their bodies also become less round and more slender as bones strengthen and muscle increases. Motor skills like fine motor coordination are practiced and improved. Cognitively, the brain grows rapidly through myelination and connections between hemispheres, supporting advances in memory, attention, and motor skills. By age 5, the brain weighs 90% of an adult's. Most children show preference for right or left handedness by the end of the preschool years.

1. Chapter 3: The Preschool Years Module 3.1 Physical Development in the Preschool Years

2. Physical Growth Growing Body: By age 2, the average child in the United States weighs around 25 to 30 pounds and is close to 36 inches tall—around half the height of the average adult. Children grow steadily during the preschool period, and by the time they are 6 years old, they weigh, on average, about 46 pounds and stand 46 inches tall.

3. Individual Differences in Height and Weight For instance, 10 percent of 6-year-olds weigh 55 pounds or more, and 10 percent weigh 36 pounds or less. Average differences in height and weight between boys and girls increase during the preschool years. Although at age 2 the differences are relatively small, during the preschool years boys start becoming taller and heavier, on average, than girls. Profound differences in height and weight between children in economically developed countries and those in developing countries.

4. Changes in Body Shape and Structure Bodies vary in height, weight, and shape Toddler fat burns off Less round and chubby and more slender Arms and legs lengthen Head size more adult-like Internal physical changes occur Muscle size increases, and children grow stronger. Bones become sturdier. The sense organs continue to develop. For instance, the eustachian tube in the ear, which carries sounds from the external part of the ear to the internal part, moves from a position that is almost parallel to the ground at birth to a more angular position. This change sometimes leads to an increase in the frequency of earaches during the preschool years.

5. Nutrition Slower growth = less caloric requirements Children can maintain appropriate intake of food, if provided with nutritious meals Inappropriate encouragement to increase food intake beyond an appropriate level may cause obesity Prevalence of obesity among older preschoolers has increased significantly over the last 20 years.

6. Nutrition (cont.) Providing a variety of foods, low in fat and high in nutritional and iron content – Foods that have a relatively high iron content are particularly important: Iron deficiency anemia, which causes constant fatigue, is one of the prevalent nutritional problems in developed countries such as the United States. High-iron foods include dark green vegetables (such as broccoli), whole grains, and some kinds of meat such as lean hamburger. Allowing development of natural preferences Exposing children to a wide variety of foods – As long as their overall diet is adequate, no single food is indispensable. Exposing children to a wide variety of foods by encouraging them to take just one bite of new foods is a relatively low stress way of expanding children’s diets.

7. Health and Illness Healthy children have about7 to 10 colds and other minor respiratory illnesses in each of years from age three to five Runny nose due to common cold is most frequent Majority of US preschoolers are reasonably healthy Minor illness permits children to understand their bodies better, to learn coping skills that will help them deal more effectively with future, more severe diseases. And to help them understand better what others who are sick are going through. This ability to put oneself in another’s shoes, known as empathy, may teach children to be more sympathetic and better caretakers.

8. Injury During the Preschool Years Before the age of 10, children have twice the likelihood of dying from an injury than from an illness. Children in the United States have a 1 in 3 chance every year of receiving an injury that requires medical attention. Danger of injuries High levels of physical activity - It is this physical activity, in combination with the curiosity and lack of judgment that also characterize this age group, which makes preschoolers so accident-prone. Curiosity Lack of judgment Individual differences Gender Cultural Socioeconomic

9. Lead Poisoning Some 14 million children are at risk for lead poisoning (Centers for Disease Control) U.S. DHHS calls lead poisoning most hazardous health threat to children under the age of 6

10. Effects of Lead Poisoning Even tiny amounts of lead can permanently harm children. Exposure to lead has been linked to lower intelligence, problems in verbal and auditory processing, and hyperactivity and distractibility. High lead levels have also been linked to higher levels of antisocial behavior, including aggression and delinquency in school-age children. At yet higher levels of exposure, lead poisoning results in illness and death.

11. Lead Poisoning Poor children are particularly susceptible to lead poisoning, and the results of poisoning tend to be worse for them than for children from more affluent families. Children living in poverty are more apt to reside in housing that contains lead paint, or to live near heavily trafficked urban areas with high levels of air pollution. Many families living in poverty may be less stable and unable to provide consistent opportunities for intellectual stimulation that might serve to offset some of the cognitive problems caused by the poisoning. Consequently, lead poisoning is especially harmful to poorer children

12. Brain Growth Grows at faster rate than any other part of the body Two-year-olds have brains that are about three-quarters the size and weight of an adult brain. By age 5, children’s brains weigh 90 percent of average adult brain weight. In comparison, the average 5-year-old’s total body weight is just 30 percent of average adult body weight. Interconnections allow for more complex communication between neurons, and they permit the rapid growth of cognitive skills Corpus callosum, a bundle of nerve fibers that connect the two hemispheres of the brain, becomes considerably thicker, developing as many as 800 million individual fibers that help coordinate brain functioning between the two hemispheres.

13. Brain Growth and Function PET scans illustrates activity in right or left hemisphere of brain differs according to task in which person is engaged

14. Brain Growth and Function Each of two hemispheres also begins to process information in a slightly different manner. Left hemisphere processes information sequentially, one piece of data at a time. Right hemisphere processes information in a more global manner, reflecting on it as a whole. In most respects the two hemispheres act in tandem. They are interdependent, and the differences between the two are minor. Even hemispheric specialization in certain tasks is not absolute. Each hemisphere can perform most of the tasks of the other. There are also individual and cultural differences in lateralization.

15. Gender-related lateralization differences Boys Greater lateralization of language in left hemisphere Higher autism incidence (Baron-Cohen’s theory) OR gender predisposition to functioning differences Girls Language is more evenly divided between two hemispheres OR Verbal abilities emerge earlier in girls because girls receive greater encouragement for verbal skills than boys

16. Gender-related lateralization differences (cont.) At birth and continuing in preschool years, boys and girls show some hemispheric differences associated with lower body reflexes and the processing of auditory information. Baron-Cohen argues that children with autism (who are predominately male) have what he calls an “extreme male brain.” Extreme male brain, while relatively good at systematically sorting out the world, is poor at understanding emotions of others and experiencing empathy for others’ feelings. To Baron-Cohen, individuals with an extreme male brain have traits associated with normal male brain, but display traits to such an extent that their behavior is viewed as autistic. Functional differences data suggest that there are minor structural differences between males’ and females’ brains. For instance, a section of the corpus callosum is proportionally larger in women than in men. Furthermore, studies conducted among other species, such as primates, rats, and hamsters, have found size and structural differences in the brains of males and females.

17. Brain Growth and Cognitive Development Myelination of the reticular formation , an area of brain associated with attention and concentration, is completed by the time children are about 5. This may be associated with children’s growing attention spans as they approach school age. The improvement in memory that occurs during preschool years may also be associated with myelination. During the preschool years, myelination is completed in hippocampus, an area associated with memory. Significant growth in nerves connecting the cerebellum , a part of brain that controls balance and movement, to the cerebral cortex , the structure responsible for sophisticated information processing. The growth in these nerve fibers is related to significant advances in motor skills that occur during the preschool years, as well as to advances in cognitive processing.

18. Motor Development

19. American Academy of Pediatrics Current Guidelines for Potty Training Dry at least 2 hours during day or after nap Regular, predictable bowel movements Indications that bowel movement or urination is about to occur Ability to follow simple directions Ability to get to bathroom and undress on time Discomfort with soiled diapers Asking to use toilet Desire to wear underwear Begin only when children are ready – usually around 24 - 36 months

20. Fine Motor Skills Involve more delicate, smaller body movements Require much practice Show clear developmental pattern

21. Handedness Preference for use of one hand over the other by end of preschool years 90% right handed More boys left-handed No scientific basis of myths that suggest there is something wrong with being left-handed. Scientists have found that the brains of left-handed people are shaped differently than those of right-handed people. Right-handers usually have asymmetric brains; their left cerebral hemispheres tend to be larger than their right hemispheres. In particular, Broca's and Wernicke's areas, two regions involved with language, are likely to be much larger in the left hemisphere than in the right. In contrast to right-handers, left-handers generally have more symmetrical brains, with similarly sized language centers in each hemisphere.

22. Becoming an Informed Consumer of Development Preschoolers should eat a well-balanced diet containing the proper nutrients, particularly foods containing sufficient protein. (The recommended energy intake for children at age 24 months is about 1,300 calories a day, and for those aged 4 to 6, it is around 1,700 calories a day.) Although some fruit juice, such as a glass of orange juice with breakfast, is fine, generally juice has so much sugar that it should be avoided. In addition, keep offering healthy foods, even if children initially reject them; they may grow to like them. Encourage preschoolers to exercise. Children who exercise are less likely to become obese than those who are sedentary. Children should get as much sleep as they wish. Being run-down from lack of either nutrition or sleep makes children more susceptible to illness. Children should avoid contact with others who are ill. Parents should make sure that children wash their hands after playing with other kids who are obviously sick . Ensure that children follow an appropriate schedule of immunizations. Current recommendations state that a child should have received nine different vaccines and other preventive medicines in five to seven separate visits to the doctor. Finally, if a child does get ill, remember this: Minor illnesses during childhood sometimes provide immunity to more serious illnesses later on.