FYI: TrekCore posted the pictures of the baby from the TWOK magazine special on Twitter today. It seems it is not Khan's baby (despite the caption from the magazine), rather, it was supposed to a baby from another of his followers.
It wasn't specified anywhere who were the parents of the child-at-the-window, nor the child in the transporter, but there was,
at some point, meant to be a young Khan child in this story. A prop was created, but ultimately unused: a painting of Marla, in self-portrait, with Khan and a child.
Complicating matters further was the fact that Judson Scott and Ricardo Montalban got together before filming, to rehearse their scenes together, and - in ignorance of the writers' intentions - developed the concept/backstory that Joachim
was Khan's son. Scott talked about it at a Brisbane convention in the 80s, and later in "Starlog".