Play (function in language acquisition) ; Spracherwerb und neurologische Entwicklung; Language acquisition and neurological development; Sprache und Denken (Ontogenese) ; Language and thought (ontogenesis) ; Cognitive development; Language acquisition and cognitive development ; Baby talk; Motherese; Child-directed speech; Ammensprache; Babysprache; Infant-directed speech; Fatherese; Language spoken to children ; Morbus Down; Mongolismus; Trisomie 21; Down's syndrome