We beleive that Aron Majer Mager is a younger brother of Moszek Mager because they both have the same last name and same address (Am Bach 27 19). Also, we found a woman named Mindla Mager, who also lived at Am Bach 27 19. She was born in 1904 (24 years before Moszek and 26 years before Aron). Therefore, we believe we have found the mother of both these children.
Since you confirmed Mindla Mager as the mother and we can't find any more information on Moszek, we have a theory that he might have been deported on the same date as Mindla. In her profile there was a ghetto note: AUSG 15.3.42 and we believe that she was deported to Chelmno because according to secondary sources, there were daily deportations to Chelmno during March 1942 and all were killed in gas vans. In your opinion, do you think it is possible that Moszek was with his mother during deportation in March 15?