Believe, the mentally retarded child same, as all other children.
Watch it to understand that gives it pleasure.
Buy to it toys for game of the house and on the street which you consider useful.
Help it to make friends with whom he with pleasure will play whenever possible every day.
Teach it to do everything that he tries to comprehend.
Extremely important to define it in the corresponding class.
If there is a suspicion on intellectual inferiority of the child, it is necessary to consult to the psychiatrist or the psychologist, resolving an issue of education of the child..