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 Rheinland-Pfalz: https://kita.rlp.de/fileadmin/kita/01_Themen/01_Wir_ueber_uns/Jugendaemter_rlp.pdf
Child protection services Rheinland-Pfalz: https://kinderrechte.rlp.de/fileadmin/MFFJIV/Familie/Kinderschutzdienste_KSD_mit_Traeger_-_Stand_November_2017_KS.pdf