Erstspracherwerb; First language acquisition; Ontogenese; Language acquisition ; Syntactic development; Morphological development; Morphologie (Spracherwerb) ; Syntax (Spracherwerb) ; Grammatical development ; Imitation (language acquisition) ; Kindersprache (pathol.) ; Child language (pathol.) ; Specific language impairment; SLI; Dysgrammatismus (Kindersprache) ; Dysgrammatism (child language) ; Handicapped language acquisition ; Dysgrammatismus; Dysgrammatism; Agrammatism ; Language intervention; Children (speech therapy with) ; Speech therapy for children ; German