The most obvious thing about children’s physical development is that they get bigger as they get older. Growth proceeds in a continuous pattern but is not smooth; the most rapid growth takes place in utero, the first 2 years of life and during adolescence (Fig. 12.1). However, acceleration and deceleration occur in response to illness and changes in nutrition or environment. As Figure 12.1 shows, infants grow very quickly in the first year of life, adding 25–30 cm to their height.

Children gain weight at an equally rapid rate, doubling birth weight by the age of 5–6 months and tripling it by the end of the first year. The birth size of a normal infant is determined by the mother. Inherited factors, however, are one of the greatest influences affecting the final stature of the child. Although children tend to attain a stature between those of their parents, some children take after one parent, a grandparent or even a more remote member of the family.

After 2 years, the rate of growth slows down and the child gains approximately 2.7 kg in weight each year until adolescence. Changes in proportion and shape take place at the same time. An adult’s head is an eighth of his total height but in a 2-year-old the head is a quarter of the total body length. In addition to this, a 2-year-old has a large body and shorter legs in proportion to that of an adult (Bee 1997).

If a child is growing and his or her shape is altering then there must be changes occurring in the child’s bones, muscles and fat. Bones increase in number, become longer and grow harder. Although bones are not all formed at birth, the newborn baby has virtually all the muscle fibres that will ever be needed. As a child grows, the muscle fibres get longer, thicker and less watery.

Development is measured using developmental scales. It is divided into four major areas:

As with growth we need to have some idea of what is the norm. The charts by Sheridan (1997) and Frankenburg & Dodds (1967) (the Denver Developmental Screening Test) were developed to show what can be expected at key stages of development. Sheridan (1997) is a little didactic, she herself suggested that her charts should be used only by experienced professionals. The Denver scale is a little more flexible, allowing the assessor to accommodate the individuality of the child, although it is suggested that the user should be trained in the use of the scale.

In the main, developmental assessments are performed by the child’s health visitor and GP, although there might be occasions when a paediatrician will also perform them. These assessments include the evaluation of:

To assess deviations from normal, it is first necessary to know about normal development. The development of a child between the ages of 0 and 18 months is very complex. These are the major milestones and their approximate age of appearance:

Activity

Watch a video showing different aspects of child development, find one at your university library or your local health promotion centre.

All aspects of development are interlinked. Skills are acquired sequentially; an example of this is the sequence of development of motor skills, which is often described as cephalocaudal, i.e. head (cephalo) to toe via the spine (caudal). So, initially, head control is developed before the baby is able to sit independently; this is followed by crawling and finally by control of the lower limbs for standing and walking. Each new skill usually appears at the most appropriate time to make use of information coming in to carry out activities to prepare for the next stage (Table 12.2).

It is important to know about child development to:

Regular respirations begin 60–90 seconds after complete expulsion from the mother as a result of both chemical and thermal stimulation. Thermal stimulation is caused by the sudden cooling of the infant leaving the warm environment of the uterus (37.7°C) and entering the cold atmosphere of the outside environment (approximately 21°C). This cooling excites sensory impulses in the skin that are transmitted to the respiratory centre. In addition, low levels of oxygen, high levels of carbon dioxide and low pH initiate impulses that excite the respiratory centre. At term, approximately 100 mL lung fluid is present within the respiratory tract. Some fluid is expelled through the mouth, assisted by the pressure on the thorax during vaginal delivery; the remainder is absorbed via the pulmonary lymphatics during the first 24 hours of life. The first breath requires a large pressure to open the terminal airways and overcome the initial stiffness of the lungs.

Separated from the placenta, the infant must make major adjustments within the circulatory system to divert deoxygenated blood to the lungs for reoxygenation. The transition from fetal to postnatal circulation involves the closure of the foramen ovale, the ductus arteriosus and the ductus venosus.

Fetal blood pressure (BP) is low as a result of low vascular resistance in the placental circuit. A systolic BP of around 76 mmHg is found at birth; this level rises to 96 mmHg by 4 weeks. Coughing, crying and straining raise the BP.

The average measurements at the 50th centile are shown in Table 12.3. The weight of the infant at birth also correlates with the incidence of perinatal morbidity and mortality. At birth, head circumference head is usually 2–3 cm greater than the circumference of the chest.

In both sexes the breasts may be enlarged in the period immediately after birth. They may also discharge clear fluid. This is due to the stimulation caused by maternal hormones; these effects subside in the first few weeks of extrauterine life (MacGregor 2000). There are nodules of breast tissue around the nipple. The testes are descended and the scrotum has plenty of rugae, the prepuce is adherent to the glans penis. The labia majora cover the labia minora.

Heat regulation is critical to the newborn baby’s survival. The baby’s capacity for heat production is adequate but several factors predispose to excessive heat loss. The newborn’s large surface area increases the possibility of heat loss to the environment, although this is normally partially compensated for by their position flexion, which effectively decreases the amount of surface area exposed to the environment. The subcutaneous fat layer is thin, giving poor insulation. This also allows transfer of core heat to the environment and cooling of blood. The hypothalamus in the brain has the capacity to promote heat production in response to stimuli received to thermoreceptors. Babies cannot shiver, nor are they able to voluntarily increase muscle activity to generate heat. Infants do produce heat by non-shivering thermogenesis and that generated by the heart, liver, brain and skeletal muscles.

Noradrenaline (norephinephrine) is secreted by the sympathetic nerve endings in response to chilling and stimulates fat metabolism in brown adipose tissue (BAT); this is unique to the newborn baby. BAT has a greater capacity for heat production through intensified metabolic activity than ordinary adipose tissue. BAT is situated between the scapulae, around the neck, in the axilla, behind the sternum, and around the kidneys, trachea, oesophagus, adrenal glands and some arteries. However, this process does require energy, so the infant’s oxygen requirement will increase. The regeneration of this tissue also requires good nutrition; a poor calorie intake will mean that the brown fat is not replaced and the infant will be less able to maintain body heat in a cool environment. Healthy, clothed infants will maintain their temperature provided the environmental temperature is maintained between 18°C and 20°C, nutrition is adequate and movements are not restricted. The temperature of the newborn is 37.5°C and by the age of 13 years it has reduced to 36.6°C; this is because infants produce more heat per kilogram body weight than older children. The temperature regulatory system is immature in the newborn infant, rendering infants and small children susceptible to temperature fluctuations. Factors such as environmental temperature, increased activity, crying or infection can cause a rapid increase in body temperature in the infant.

At birth, the eyeball is too short for its lens therefore babies focus best at approximately 20 cm (Fig. 12.8). As the eyeball continues to grow, distance vision is achieved. The ciliary muscles are immature, limiting the ability of the eyes to accommodate and fixate for any length of time. Babies have been shown to demonstrate visual preferences for some colours rather than others. No tears are present and eyes are easily infected. Corneal, papillary and blink reflexes are present.

Once the amniotic fluid is drained from the external ear canal the acuity is similar to that of an adult. Babies can detect pitch, loudness and timbre of sound in addition to location and changes in complex sounds. The internal and middle ear is larger in proportion at birth and the external canal small. The mastoid process and the bony part of the external canal have not yet developed. The tympanic membrane and facial nerve are close to the surface and easily damaged.

The respiratory system is developmentally incomplete. The lungs mature after birth and new alveoli continue to grow for many years. There are 20 million alveoli at birth, increasing to 300 million alveoli in the fully formed lungs of the adult (Meadow & Newell 2002). This means that infants and young children have a relatively small alveolar surface area for gaseous exchange. Airway resistance in children is high due to the small diameter of the respiratory tree. The lumen of the peripheral airways is narrow, which predisposes the infant to airway obstruction. The infant’s breathing is mainly abdominal: the abdomen distends, the diaphragm contracts and the thorax expands. The chest wall is very compliant and therefore easily distorted, which can increase the work of respiration.

Babies are obligatory nose breathers and do not convert automatically to mouth breathing when nasal obstruction occurs. Respiratory rate is 30–60 per minute. Respirations are shallow and the pattern alters during sleeping and waking. Many term babies have periods of rapid breathing alternating with periods of breathing at a slower rate, or they may not breathe for periods of up to 15 seconds – this is normal as long as the colour and heart rate do not change significantly and the infant then begins to breathe again spontaneously (MacGregor 2000). Periods of apnoea, when breathing ceases for more than 20 seconds, are only common in babies under 32 weeks’ gestation unless there is an underlying condition.

The heart rate is roughly 120–160 beats per minute and fluctuates with respiratory function, activity and sleep. It reaches a maximum at month, after which there is a gradual slowing until adult levels at 12–16 years of age. Peripheral circulation is sluggish and there may be mild cyanosis of hands and feet with mottling of skin when exposed.

Normal blood pressure ranges between 50/25 and 70/40 mmHg. The amount of total circulating blood is 80 mL/kg or approximately 300 mL at birth. Haemoglobin (Hb) = 15–20 g/dL; 70% is fetal Hb, which is replaced by adult Hb in the first 2 years of life. Mean cell volume (MCV)/100 L = 135 femtolitres = 10 ⁻¹² g.

Breakdown of excess red blood cells in the liver and spleen predisposes to jaundice in the first few weeks. Prothrombin levels are low due to a lack of vitamin K. Colonisation of the intestine promotes synthesis of vitamin K. The white cell count is initially 18 × 10 ⁹/L and reduces rapidly. Cardiac output is related to the heart rate and the stroke volume; as children have smaller hearts the stroke volume is reduced. The heart then needs to beat faster in order to oxygenate their body tissues.

The newborn baby’s kidneys weigh 23 g; this will have doubled by 6 months and trebled by the end of the first year (Sinclair 1991, cited in MacGregor 2000). The renal system is functional before birth but the workload is minimal. The infant is not able to concentrate or dilute urine very well in response to variations in fluid intake, and cannot compensate well for high or low solutes in blood. The ability to excrete drugs is also limited. However, the newborn can excrete amino acids and conserve sodium and glucose. The glomeruli are immature; they are resistant to aldosterone, which results in limited ability to concentrate the urine. This lack of ability to conserve or excrete water makes the baby vulnerable to dehydration. The glomerular filtration rate is 30 mL/min/m ² at birth, 100 mL/min/m ² at 9 months, and reaches adult values at year (Davenport 1996, cited in MacGregor 2000). Dehydration, hypotension and hypoxaemia all produce a fall in glomerular filtration rate, so renal function becomes compromised very quickly in a crisis. Urine is voided by reflex emptying of the bladder. The first urine is passed either at birth or during the first 24 hours and then increases in frequency as the fluid intake increases. The specific gravity should be 1.020. After birth, the kidneys increase in size in proportion to body length, the weight doubling in the first 10 months as a result of tubular growth.

The endocrine system produces limited quantities of antidiuretic hormone from the posterior pituitary gland, thus making the infant more susceptible to dehydration. The effect of maternal hormones may cause the labia to be hypertrophied and the breasts engorged.

This system is structurally complete but functionally immature. The teeth are usually still buried in the gums. Sucking pads in the cheeks give them a full appearance. Sucking and swallowing reflexes are coordinated.

The stomach’s capacity at birth is approximately 10–20 mL, although this increases rapidly in the first few weeks of life up to 150 mL by 1 month. The cardiac sphincter is weak, making the baby prone to regurgitation or possiting and gastric emptying time is 2.5–3 hours. Hydrochloric acid is present in the stomach at birth but, due to swallowing of amniotic fluid, the pH is nearly neutral. Acid secretion commences within 8 hours of birth and digestion in the stomach is then reliant on the action of hydrochloric acid and rennin to cause the formation of curds by coagulating the casein in milk. Human milk contains e-fructose, a bacterium that raises the acidity of the gut inhibiting the growth of Escherichia coli bacteria. Adult levels of acid secretion are reached by the age of 10 years.