There are different state achievements You might be eligible for: separate maintenance/alimony, child benefit, parental benefits or housing benefit.
The cases are all treated individually, please contact the local authorities and counseling centers.
Information and consultation in Brandenburg:
General information: http://www.masgf.brandenburg.de/cms/detail.php/bb1.c.215903.de
Holiday grants: http://www.lasv.brandenburg.de/sixcms/detail.php/652499
Help for Families in Need - Foundation of Brandenburg: http://www.masgf.brandenburg.de/sixcms/detail.php/bb1.c.220607.de
Association of single mothers and fathers Brandenburg: http://www.vamv-brandenburg.de/VAMV-Landesverband:::1.html