Children are affected by certain diseases that cause small children to be significantly thinner compared to normal children. Apparent thinness in children is one of the clinical symptoms of congenital heart disease. Infants with congenital heart disease significantly lag behind children of the same age in terms of development, manifesting as thinness, malnutrition and growth retardation. Congenital cardiovascular disease is the most common type of congenital malformation. With the advances in cardiac diagnostic methods and surgical treatment techniques, the majority of congenital cardiovascular diseases can now be clearly diagnosed and surgically corrected, and the prognosis is significantly improved compared to the previous ones. This is due to the disturbance of the fetal heart during the development process, making some of the development stop or defect, as well as some of those who should degenerate fail to degenerate completely. In addition, amniotic membrane lesions, mechanical compression around the fetus, maternal nutritional disorders, vitamin deficiency and metabolic diseases, maternal use of cytotoxic drugs or Longer radiation exposure, may be related to the occurrence of the disease. Genetic factors 5% of patients with precordial disease occur in the same family with the same or similar disease, which may be due to genetic abnormalities or chromosomal aberrations. Third, other Highland areas have a higher incidence of patent ductus arteriosus and atrial septal defect, the occurrence of which may be related to hypoxia. Some precordial diseases are gender predisposed. Fetal period: The mother does not pay attention to pregnancy nutrition and health care during pregnancy, resulting in fetal stunting. The infant is born at a lower than normal height and weight, which directly leads to thinness in childhood. Neonatal period: Inadequate feeding during the neonatal period is another reason why children are too thin. During the neonatal period, especially the week after birth, if the calorie deficit, insufficient nutrition will lead to the entire childhood growth and development lag. Therefore, during the newborn period must let the child eat enough, if artificial feeding, the concentration of milk powder must be in accordance with the scientific ratio. Infancy: If parents do not give their infants the necessary supplementary food in a timely and reasonable manner, resulting in insufficient total calorie intake to meet the needs of rapid growth and development, is also the cause of children thin. Early childhood: This stage of the child, thinness is mainly due to poor eating habits, such as snacking too much to affect the appetite of the main meal, picky eater and so on. Other causes: Micronutrient deficiency. The most important element that can affect the growth of children is zinc. Zinc deficiency can reduce your child’s appetite. Therefore if your child is thin you should go to the hospital to be checked for zinc deficiency. Pathological factors: Having congenital diseases such as hypertrophic pyloric stenosis; having chronic diseases such as iron deficiency anemia, tuberculosis, recurrent respiratory infections, glomerulonephritis, rheumatic fever, protein-energy malnutrition, etc. can make a child become thin and small.