The first contact for safety issues is the police authority (call number 110). In case of a risk to the child's well-being through neglect or mistreatment the Youth Welfare Office (General Social Service) should be contacted.
Youth welfare offices in Berlin: https://service.berlin.de/standorte/jugendaemter/
The youth welfare offices have a telephone emergency service https://www.berlin.de/sen/jugend/familie-und-kinder/kinderschutz/#notdienste