It was Agatha all along...

Sailorsaint said
I think Agatha knows more about the kid than she is letting on, or at least has a strong suspicion.
Click to expand...
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!!!!