The body size differences are paralleled by maturation changes. The smaller body of an infant or neonate is substantially different physiologically from that of an adult. Congenital defects, genetic variance, and developmental issues are of greater concern to pediatricians than they often are to adult physicians. A common adage is that children are not simply “little adults”. The clinician must take into account the immature physiology of the infant or child when considering symptoms, prescribing medications, and diagnosing illnesses.

Pediatric physiology directly impacts the pharmacokinetic properties of drugs that enter the body. The absorption, distribution, metabolism, and elimination of medications differ between developing children and grown adults. Despite completed studies and reviews, continual research is needed to better understand how these factors should affect the decisions of healthcare providers when prescribing and administering medications to the pediatric population.

Infants as a form of basic instinctive communication. A crying infant may be trying to express a variety of feelings including hunger, discomfort, overstimulation, boredom, wanting something, or loneliness.

Adequate food consumption at an early age is vital for an infant’s development. The foundations of optimum health, growth, and neurodevelopment across the lifespan are established in the first 1000 days of life. From birth to six months, infants should consume only breast milk or an unmodified milk substitute. As an infant’s diet matures, finger foods may be introduced as well as fruit, vegetables, and small amounts of meat.

As infants grow, food supplements are added. Many parents choose commercial, ready-made baby foods to supplement breast milk or formula for the child, while others adapt their usual meals for the dietary needs of their child. Whole cow’s milk can be used at one year, but lower-fat milk is not recommended until the child is 2 to 3 years old. Weaning is the process through which breast milk is eliminated from the infant’s diet through the introduction of solid foods in exchange for milk. Until they are toilet-trained, infants in industrialized countries wear diapers. The transition from diapers to training pants is an important transition in the development of an infant/baby to that of a toddler. Children need more sleep than adults—up to 18 hours for newborn babies, with a declining rate as the child ages. Until babies learn to walk, they are carried in the arms, held in slings or baby carriers, or transported in baby carriages or strollers. Most industrialized countries have laws requiring child safety seats for babies in motor vehicles.

Benefits of touch

Studies have shown that infants who have been the recipients of positive touch experience more benefits as they develop emotionally and socially. Experiments have been done with infants up to four months of age using both positive touch (stroking or cuddling) and negative touch (poking, pinching, or tickling). The infants who received the positive touch cried less often and also vocalized and smiled more than the infants who were touched negatively. Infants who were the recipients of negative touching have been linked with emotional and behavioral problems later in life. A lower amount of physical violence in adults has been discovered in cultures with greater levels of positive physical touching.

Language development

Caregivers of an infant are advised to pick up on the infant’s facial expressions and mirror them. Reproducing and empathizing with their facial expressions enables infants to experience effectiveness and to recognize their own actions more easily. Exaggeratedly reproduced facial expressions and gestures are recommended, as they are clearer forms of expression. The baby’s babbling should also be picked up and repeated. By imitating each other’s sounds the first simple dialogues are initiated. Accentuated pronunciation and melodic intonation make it easier to recognize individual words in a sentence. However, it is not advisable to use simplified “baby language” (e.g., “Did you ‘ouch’?” instead of, “Did you hurt yourself?”).

Even if parents cannot yet understand infants’ babbling, a timely response by parents to babbling leads to faster language acquisition. This was confirmed by researchers who first studied mothers’ behavior towards 8-month-old infants and later tested the infants’ vocabulary when they were 15 months old. A first important development of infants is the discovery that they can influence their parents through babbling (development of intentional communication). Parents can encourage this by engaging with their infants in babbling. This in turn promotes further language development, as infants then turn to their parents more often.

Previous studies have shown that the infant’s speech is encouraged when parents, for example, smile in the infant’s direction or touch the infant every time the infant looks at them and babbles. It also helps if parents respond to what they think their baby is saying (for example, giving a ball or commenting when the baby looks at the ball and babbles). Responding to sounds produced when the baby looks at an object (object-directed vocalizations) thus provide an opportunity to learn the name of the object. In this way, babies also learn that sounds are associated with objects. However, language development is only achieved if parents react positively (e.g. smile) in response to the infant’s babbling. A high response rate without a connection to the infant’s utterances does not lead to language promotion. It is detrimental to language development if a mother instead tries to divert the infant’s attention to something else.

Sleep

A 2018 review analyzed 146 studies on infant sleep behavior and listed several factors that show an effect on sleep duration and the number of night waking. For example, stimulating daytime activities, reading aloud before sleeping, early bedtime, a sleep routine, and avoiding television and media exposure before bedtime are associated with longer sleep duration and fewer nighttime awakenings.

Furthermore, strong parental involvement at falling asleep is associated with shorter sleep duration, slower falling asleep and more frequent night-time awakenings in the studies analyzed. Strong parental involvement is understood to include parental presence, cradling, or breastfeeding at bedtime, as well as carrying the infant to sleep and then putting the infant down. Strong parental involvement has a negative effect on infant sleep because the infant cannot develop the ability to self-soothe. On the other hand, low parental involvement at bedtime gives the infant room to learn self-soothing and self-regulation.

In 2020, a Finnish study established (according to the research leader) for the first time a reference value for infant sleep quality based on a large data set (about 5,700 babies). Almost 40% of the participating parents with eight-month-old babies said they were worried about their sleep. In fact, sleep problems were common; however, children fall asleep faster, wake up less often during the night and stay awake less late at night the older they get. At the same time, total sleep time decreases.

The study was also able to determine reference values for normal sleep. Children who sleep significantly less than average would usually benefit from supportive measures, for which a number of methods would be available (a discussion with the pediatrician or see, for example, the article on sleep training).

Maternal sensitivity

Maternal sensitivity plays a particular role in the relationship with the infant and for favorable emotional development. This means being attentive to the infant’s behavioral expressions, not misinterpreting the infant’s expressions because of one’s own moods, reacting immediately to the situation and finding a response that is appropriate to the context and the expressed needs. A secure attachment is promoted through empathetic and adequate as well as prompt responses. In accordance with their basic needs, infants show an inborn behavior of seeking closeness to the mother – or to another primary caregiver – and thus in turn foster an attachment. When separated from the mother, infants protest by crying and by body movements.

Carrying has a calming effect on infants. A 2013 study showed that infants placed in a cradle cried and kicked more often and had an increased heart rate (so the infants were stressed), while those picked up and carried by the mother while walking around calmed down significantly. The effect of being held motionless in the arm was intermediate between that of being carried around and that of being put down. That carrying (e.g., in a baby sling) makes infants more content and makes them cry less had already been shown in a randomized study.

For infant feeding, breastfeeding is recommended by all major infant health organizations, if you are physically and emotionally able to breastfeed.

Emotional development

Attachment theory is primarily an evolutionary and ethological theory whereby the infant or child seeks proximity to a specified attachment figure in situations of alarm or distress for the purpose of survival. The forming of attachments is considered to be the foundation of the infant/child’s capacity to form and conduct relationships throughout life. Attachment is not the same as love or affection although they often go together. Attachment and attachment behaviors tend to develop between the age of 6 months and 3 years. Infants become attached to adults who are sensitive and responsive in social interactions with the infant, and who remain as consistent caregivers for some time. Parental responses lead to the development of patterns of attachment, which in turn lead to ‘internal working models’ which will guide the individual’s feelings, thoughts, and expectations in later relationships. There are a number of attachment ‘styles’ namely ‘secure’, ‘anxious-ambivalent’, ‘anxious-avoidant’, (all ‘organized’) and ‘disorganized’, some of which are more problematic than others. A lack of attachment or a seriously disrupted capacity for attachment could potentially amount to disorders.

Infants develop distinct relationships to their mothers, fathers, siblings, and non-familial caregivers. A good quality of the triadic relationships (mother – father – infant) is important for infant mental health development.

Response to sounds

Infants respond to the sound of snake hissing, angry voices of adults, the crackling sound of a fire, thunder, and the cries of other infants. They have a drop-in heart rate, their eyes blinking, increased turning toward the speakers or parent, all of these indicating that they were paying more attention. This is believed to be an evolutionary response to danger. Babies’ ability to accurately locate sounds is refined during their first year.