Four-month-old baby’s neck is very soft may be due to pediatric Down’s syndrome, rickets, cerebral palsy and other diseases. 1. Pediatric Down syndrome: this disease is caused by an abnormality of chromosome 21, and common predisposing factors include genetics, maternal age, exposure to radiation during pregnancy, and viral infections. Since the children will have growth retardation and hypotonia, some four-month-old children will have a very soft neck. 2. Rickets: Because rickets will lead to abnormal muscle metabolism, so that the whole body muscle relaxation, muscle tone is weakened, so some of the serious condition of the four-month-old child will have a very soft neck performance. 3. Cerebral palsy: studies show that this disease may be related to early pregnancy infection, premature birth, hypoxia, hyperbilirubinemia, brain trauma, genetics and other reasons. The main symptoms are motor dysfunction, delayed loss of primitive reflexes, hypotonia, etc. As a result, the affected child may have a very soft neck. Four-month-old baby’s neck is very soft may also have other causes, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.