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.
Niedersachsen
Youth offices Niedersachsen: https://www.kinderinfo.de/jugendaemter/mecklenburg-vorpommern/
Child protection hotline 0800 - 14 14 007
Child protection Niedersachsen: http://www.kinderschutz-niedersachsen.de/?08FE203FEBE3E771E2A28271CE92EA45
Child Protection Center Hannover: http://www.ksz-hannover.de/Start/c/100
Child Protection Center Oldenburg: https://www.kinderschutz-ol.de/