Columbia subject headings:
Harvard subject headings:
Education, Preschool--Germany--Bochum--History.
Education, Preschool--Germany--Cologne--History.
Education, Preschool--Germany--Krefeld--History.
Princeton subject headings:
Education, Preschool--Germany--Bochum--History.
Education, Preschool--Germany--Cologne--History.
Education, Preschool--Germany--Krefeld--History.