First, it is difficult to eat milk: it appears in infancy. The earliest symptoms of infants with mental retardation are often difficult to breastfeed, unable to suck, and particularly prone to vomiting, indicating that the nervous system is damaged and their intelligence will be affected in the future.

2. Abnormal face and posture: Some babies with congenital mental retardation have abnormal face and posture. For example, children with congenital stupidity have wide eye distance, squint eyes, flat nose, tongue dragging out of mouth, drooling and other manifestations, which is often called "international face". Children with hydrocephalus have a particularly large head circumference, and children with microcephaly have a particularly small head. The body of hypothyroidism is particularly short, and the skin of phenylketonuria is unusually white and the hair color is particularly light.

Third, the movement is slow: the mentally retarded baby is obviously slower than the normal baby. The starting age of prone head, sitting, standing and walking is later than that of normal children of the same age. Especially when walking, it is more obvious. You often have to be 3-4 years old or 4-5 years old to walk on your own, and you can't walk steadily.

Fourth, language development is backward: normal babies can imitate sounds in 7-8 months, call their parents around one year old, speak more than a dozen words at one and a half years old, understand simple instructions, ask simple questions around 1 year old, and basically express their ideas around 1 year old. Those who are four or five months behind, or even l-2 years behind, should be regarded as the performance of mental retardation.