I'm very sorry for the long wait - I had to talk to our law expert in order to provide you with the correct information.
Last time we talked, I shared some sources with you regarding the process of getting a residence permit through your German child. One of the prerequisites is to have proof of a main residence in Germany (e.g. Berlin).
Please note that you need to have a legal status in Germany to receive said proof or to be able to apply for a residence permit in general! Since you stated before that you do not have a legal status yet, it is essential that you discuss your case with a lawyer or legal aid service (if you haven't already done so).
If you have any more questions after you talked to them, feel free to reach out to the community again :-)
All the best,