Facts:

In 2008 my unmarried gf gave birth to our first child in Thailand.

She had been residing in Thailand since her birth in 1987, but has no Thai citizenship, she is not listed in any house registry, only has an ID card (actually on the back it says it is not an ID card, but is to be shown whenever dealing with officials) issued by the ministry of the interior, which looks like the normal ID card any thai has, only that it is white on the front and pink on the back and the number starts with 0. In my opinion she actually is entitled to thai citizenship, only does not have it because of her own and parents' ignorance and the lack of assistance to illiterate hilltribe people by the officials in the amphur office.

I myself have german citizenship and had been in Thailand on a tourist visa.

At the hospital we were given a "birth certificate for a child of a person without registration status", our childs ID number on the birth certificate starts with 1, but there is no entry regarding citizenship.

I believe, that our child may have a claim to thai citizenship, because it was born in Thailand and the mother had been residing in Thailand.

Am I correct? What steps would we have to take first?

Thanks for any helpful advice.

Get you gf Thai citizenship first. Heard before; that typically it is easy to sort this out with amphur office before a person turns age 16. After that it becomes more difficult and complicated by bureaucracy. Judge, to gain Thai citizenship, person must prove that both she and one of her parents were born in Thailand. Lack of documentation in remote areas and or villages makes this constraint a complex difficulty. Person needs to prove that one of her parents was born in Thailand, sometimes must also prove that one of her grandparents was born in Thailand. Keep trying with the amphur hall of her parents. Persistence pays off. Good luck.

Get you gf Thai citizenship first. ... Keep trying with the amphur hall of her parents. Persistence pays off.

Had been trying that for almost two years unsuccessfully. The officers are extremely reluctant to create any precedent for granting citizenship, I guess.

Frequenting the amphur is quite impossible at the moment too, since we are currently in Germany (gf has travel document for stateless persons issued by german government).

Regarding my gf we will probably need some kind of birth certificate for her soon, which we have so far been unable to get from the amphur. We will need it, because we are expecting our second child and the local registrar demands the mothers birth certificate in order to issue a birth certificate for the child. Without birth certificate for the child we cannot get it into our health insurance and we need it for the application of the child bonus from the government.

There is no Thai citizenship for children born in Thailand, (besides a few exceptions not counted and which don't apply to your case). The only thing what would make the child Thai is if one of the parents had Thai citizenship when the child was born.