Congenital dementia is a defect in mental activity in preschool children in the development of thinking, memory, speech, praxis and affective development over a relatively long period of time before full maturation. With congenital dementia there is a delay in speech development. Speech development in children may be delayed or absent. In such cases, they talk about aphasia or oligophrenia (and also about mental retardation and other things). Levels of developmental delay range widely from mild loss of communication to severe loss of self-care. For the same group of children, vocabulary depends on how fully the child is taught to use it. A child with an intellectual disability needs more speech material than a normally developing child. Understanding speech in dementia will depend equally little on the number of words used. As we see from what is described above, the separation of the concepts of “dementia” and “mental retardation” is in fact quite justified. Children with dementia are distinguished from children with general retardation by clearer signs. It is this difference that teachers of inclusive preschool institutions rely on in the selection of personnel. Childhood autism is just such a case when, along with basic medical and psychological help, special help from a teacher is needed to effectively organize life in a group in which there are hearing-impaired children, as well as to organize interaction with specialists in order to correctly diagnose the condition and conduct a course rehabilitation. The peculiarities of a defectologist for working with such children lie in the fact that the teacher must have a complete understanding of Down syndrome, first of all.