They want to believe that he's the child she gave up to get the Darkhold. Thanks to @Eeyore , I think the kid is the 4th name on the list that was given to Agatha, Blackheart...The Son of MEPHISTO!!!!
There was a supposed funko pop leak that spoils who he is, and he's not Blackheart. They also spoiled who Aubrey is. I can put it in spoiler tag if y'all want me to say who these leaks say they are.