Welcome to the Wefugees Community and thank you for reaching out to us. First of all, I am very sorry to hear about the child's bad situation and I can imagine how difficult it must be for the parent here in Germany.
Unfortunately, I can not think of a possible solution of this problem for the time being. The family reunification (visa) process is not possible as long as the asylum procedure is still ongoing and the decision on the application pending (with the family reunification within the EU in the context of the Dublin regulations as exception). In case the parent will get accepted as refugee (or get the "subsidiary protection") in Germany, the minor may be able to get a visa. Since this process can be quite complicated as well (both parents need to agree or it needs to be proven that the parent in Germany has the sole custody etc.), it is highly recommended to get support in an experienced refugee/migration counselling office.
As I am based in Germany and I am not familiar with the immigration/residence law in Poland, for instance, I can not exclude that a visa process might be theoretically possible outside of Germany. In any case, I think it will be important for you to get in contact with an already mentioned counselling office in order to assess your individual situation and the options in detail. There are numerous counselling offices all over Germany where you can receive free of charge, professional and confidential counselling. Please let uns know if you need help in finding such an office in your area.
I will also link my colleages dear @mbeon-fardeen and @mbeon-Éanna here, maybe they have another idea or correct me if needed. However, also don't hesitate to get back to us with any further questions.
All the best,