Kindergeld is a benefit offered through the Income Tax Law and is available to children of German residents from birth until the age of 18 in most cases. There are some circumstances that allow payments until child is 25 years of age. Applications for kindergeld are filed with the Familienkasse (Family Benefit Office) of the Bundesagentur für Arbeit (Federal Employment Agency).
Resident permit(s) and working permit(s) copies are required to be sent in with the paper work.
The Bundesagentur für Arbeit website is helpful and has some information in English, however much of the info in German as well as the forms (thank goodness for Google translate!). http://www.arbeitsagentur.de/nn_426328/EN/Navigation/Startseite/Startseite.html
In Frankfurt the office contact information;
Agentur für Arbeit Frankfurt am Main
60311 Frankfurt am Main
Servicetelefon 01801 54 63 37
Kindergeld (0 69) 2171 28 23
Office Hours: Monday - Wednesday 8-12, Thursday 8-6, Friday 8-12
From what I understand Kindergeld is one of the "social" programs that Germany has to encourage people to procreate - at least that is the view of one of our German friends. Elterngeld and Mutterschaftshilfe are also a part of the benefits of having a baby in German, if you are eligible. More on those later.