Basically it is possible to apply for an unlimited residence (Niederlassungserlaubnis), if your German child is more than 3 years old and you live with him the whole time. But the problem is that, even if you earn enough and the family has no social help, you must have paid to a pension fund for 60 moths before application, which is not possible if you have worked in Germany for less than 5 years. I only don't know if it is possible to add payments in another country, provided you paid to such a fund in another country before.
Residence Act, Section 28
Subsequent immigration of dependants to join a German national
(2) As a rule, the foreigner is to be granted a permanent settlement permit if he or she has
possessed a temporary residence permit for three years, the family unit with the German
continues to exist in the federal territory, there is no public interest in expelling the foreigner
and the foreigner has a sufficient command of the German language. Section 9 (2)
sentences 2 to 5 applies accordingly. In all other cases, the temporary residence permit is
extended as long as the family unit continues to exist.
You must have B1 German certificate.
And the following conditions from Section 9 must be fulfilled:
2. the foreigner’s subsistence is secure,
3. the foreigner has paid compulsory or voluntary contributions into the statutory
pension scheme for at least 60 months or furnishes evidence of an entitlement to
comparable benefits from an insurance or pension scheme or from an insurance
company; time off for the purposes of child care or nursing at home are to be duly taken
4. there are no reasons of public safety or order which would rule out granting
such a permit, taking into account the severity or the nature of the breach of public safety
or order or the threat posed by the foreigner, with due regard to the duration of the
foreigner’s stay to date and the existence of ties in the federal territory,
5. the foreigner is permitted to be in employment, if he or she is an employee