The fontanelle is the bone gap formed by the skull joint of infants and young children, and there is a difference between the fontanelle and the bregma. The fontanelle is located in the front of the top, in the shape of a diamond, and closes at about 1-1.5 years of age after birth, while the posterior fontanelle generally closes three months after birth, and the fontanelle that people usually refer to is mainly the fontanelle. Under normal circumstances, the size of a baby’s fontanel is about 1.5 cm x 2 cm, from the surface, the fontanel is flat or slightly sunken, after birth, as the baby grows up, the fontanel will increase slightly with the gradual increase in head circumference, after 6 months, due to the gradual ossification of the skull, the fontanel will gradually become smaller, and at the age of 1 to 1.5 years, the fontanel will be basically closed. If a baby’s fontanelle sinks within a short period of time, the most common reason is a lack of water in the baby’s body. If this symptom occurs after a baby has diarrhea or vomiting, it indicates that the body has been moderately dehydrated, and in order to lower the baby’s intracranial pressure, large doses of dehydrating agents are used, thus causing the fontanelle to sink. The degree of dehydration should be supplemented with fluids for the baby to avoid metabolic disorders caused by excessive dehydration. If the baby is malnourished and thin due to improper feeding, the baby will also have the phenomenon of sunken fontanelle, so it is necessary to strengthen nutrition and have a reasonable diet, and this phenomenon will disappear when the baby’s nutrition keeps up. In summary, parents must pay attention to the nutritional supplements of their children and feed them reasonably, and let them eat more foods rich in vitamins to ensure their healthy growth.