Dear @Musawvir,
Thank you for sharing your question with the Wefugee Community!
If your child is German, you can apply for a children travel document ("Kinderreisepass") in the Bürgerservice Office in Lübeck. Their website is listing the required documents, i.e. the birth certificate, a written declaration of consent, a biometric picture of the child, and the ID of the parents.
I hope this helps and all the best,
Meike