The growth and development of children is a continuous and progressive dynamic process and should not be artificially fragmented. However, over the course of growth, children exhibit age-related patterns in anatomical, physiological, and psychological functions at different stages. For practical purposes, the stages of childhood are divided into seven periods to facilitate understanding and application.
Fetal Period
The conventional method for calculating the fetal period is from the first day of the mother’s last menstrual period until birth, spanning 40 weeks. However, in stricter terms, the entire developmental process of the fetus should be calculated from fertilization to birth, lasting 38 weeks. The age of the fetus is referred to as the gestational age. During pregnancy, adverse external factors such as infections, trauma, misuse of medications, exposure to radiation, or substance abuse, as well as maternal nutritional deficiencies, severe illnesses, and psychological trauma, may affect the normal growth and development of the fetus. These influences can result in miscarriage, congenital malformations, or intrauterine growth retardation.
Neonatal Period
The neonatal period refers to the time from cord clamping and detachment from the mother after birth until the 28th day. Based on age classification, this period technically falls within the infant period. However, it is recognized as a distinct stage due to its unique characteristics in growth, development, and disease susceptibility. The neonatal period is marked by high morbidity and mortality. During this time, the infant transitions from maternal dependence to independent survival, accompanied by fundamental changes in internal and external environments, though their adaptive capabilities remain immature. Birth-related injuries, lingering infections, and congenital malformations are commonly evident during this stage.
Infant Period
The infant period spans from birth to the first birthday. This stage is characterized by rapid growth and development, with relatively high nutritional demands. While all organ systems continue to grow and develop, they remain immature, particularly the digestive system, which often struggles to adapt to the digestion and absorption of large quantities of food. Digestive dysfunctions are thus common. Additionally, maternal antibodies gradually decline, while the infant’s own immune system is still underdeveloped, making them more susceptible to various infections.
Toddler Period
The toddler period covers ages from one year to just before the third birthday. Growth and development during this stage slow down slightly compared to the infant period, while cognitive and intellectual development accelerate. Increased mobility and broader exposure to social interactions occur during this period. However, digestive system functions remain immature, and nutritional demands remain relatively high. As weaning and the transition to alternative foods usually occur during this stage, appropriate feeding practices are critical for maintaining normal growth and development. Toddlers exhibit limited awareness of risks and self-protection, resulting in a high incidence of accidental injuries.
Preschool Period
The preschool period spans from three years of age to six or seven years, until the child enters primary school. Physical growth during this stage slows further and adopts a steady pace, while intellectual development progresses rapidly. Children expand their interactions with peers and the broader social environment, broadening their knowledge base. Self-care skills and preliminary social abilities are also cultivated during this stage.
School Age Period
The school age period begins with primary school entry (at six or seven years of age) and lasts until the onset of adolescence. During this period, physical growth remains relatively slow, and all organ systems—except for the reproductive system—take on an adult-like appearance. Intellectual development becomes increasingly mature, and children are able to receive systematic education in scientific and cultural disciplines.
Adolescence Period
The adolescence period typically ranges from 10 to 20 years of age and serves as a transitional stage from childhood to adulthood. This period encompasses a series of endocrine changes that lead to sexual maturation and the development of reproductive capabilities. It is also a time of physiological, psychological, and emotional development. Girls generally enter and complete adolescence about two years earlier than boys. There is significant individual variation in the onset and conclusion of adolescence, with differences of two to four years being common. During this stage, physical growth accelerates again, reaching a second peak, and the reproductive system undergoes rapid development towards maturity.