Gesture communication ; Case study (language acquisition) ; Kindersprache (pathol.) ; Child language (pathol.) ; Specific language impairment; SLI; Dysgrammatismus (Kindersprache) ; Dysgrammatism (child language) ; Handicapped language acquisition ; Spracherwerb (lex.) ; Language acquisition (lex.) ; Vocabulary (language acquisition) ; Case study (pathol.) ; Morbus Down; Mongolismus; Trisomie 21; Down's syndrome ; Language intervention; Children (speech therapy with) ; Speech therapy for children