Gender: boy
I searched for J. Birenfeld and there were three results. I narrowed down the results to one boy who was born between the correct years of 1921 and 1927. He was JAN ZBIGNIEW BIRENFELD and he was born 11 Oct 1925 and he lived at HOHENS 38 flat 16 and PIRAMOWICZA 5.
I found only LUCIA FELIKSA BIRENFELD born 7 Feb 1898 living at the same address. I found Jan in the Work Cards and he was listed with worker number 8386 and worked as a Bürobeamter at 26 Rembrandtstr. (Schneiderei) 14. I also found his mother as Lucja Feliksa in the work cards and she was a "Kanzleiarbeiterin."
I couldn't find anymore information on Jan or his mother in the following stages.