Children with different degrees of mental retardation show different symptoms, which are divided into mild, moderate, severe, and very severe, as follows: I. Children with mild mental retardation: mild defects in adaptive behavior, slightly later development in early life than normal children, but not as lively as normal children, whose speech development is slightly delayed, poor analytical ability, and poor academic performance, such as being able to recite texts, but not apply them. Children with moderate mental retardation: the development of the whole child is slower than normal children, the words are unclear, only simple concrete thinking can be carried out, the ability to discriminate the surrounding environment is poor, and they can only recognize the surface phenomenon of things. Children with severe mental retardation: delayed development in all aspects, vague pronunciation, very little speech, low comprehension, very clumsy movements, and the ability to avoid obvious dangers. IV. Children with very severe mental retardation: they do not understand everything around them, they only call out to dad and mom, but are unconscious, have significant motor impairment, often with multiple disabilities or epilepsy, and are unable to take care of themselves in their personal lives.