Dear Salome Mkota,
Welcome back to the Wefugees community and thank you for reaching out to us again.
I agree with @Elvis: A German birth certificate does not present necessarily a German citizenship. The father needs to acknowledge the paternity. Is he mentioned in the birth certificate? If not, the child can not have the German citizenship yet. Maybe you can have a closer look at the document and get back to us with more details.
I hope this helps and all the best,