Dear @Leon, Thank you for reaching out to the Wefugees Community.
If I understand you correctly, your baby was born in Germany? In that case, the German authorities should have issued the birth certificate accordingly, right?
However, if you, as parents, both live in Germany, the „Jugendamt“ will also be responsible for the custody issues. Please find more details on this website (describing the procedure in Berlin though): https://service.berlin.de/dienstleistung/326590/.
If required documents are issued in Polish language, you might need a professional translation. As long as you can provide all papers, I don’t see any problems regarding the declaration of custody - even if documents are from Poland.
Would you agree @Infoverbund or @mbeon-Christine?
Please get back to us with any further questions or if any clarification is needed.
All the best,