I don't really understand. Do these pictures mean that there was a deleted scene featuring the described script lines? Why wasn't it used? And what does this child have to do with the Genesis device?
There was also a set decoration created of a painting of Marla, Khan and child, but it was not seen onscreen.
Yes, there was a concern that the film's rating would have been affected if the child had gone kablooey with Reliant.
Wasn't the other discussion about Joachim/Joaquin being Khan's son?
I got to spend a week entertaining Judson Scott when he was in Australia for a convention in the 80s. He said that he and Ricardo Montalban used to get together to rehearse, before filming commenced, and that the angle they developed was that Khan and Joachim were father and son. But that didn't necessarily agree with the script or novelization.
It's more likely that Joachim was Joaquin (Mark Tobin from "Space Seed")'s son. And this is the angle used by Greg Cox's novel "To Reign in Hell". Also in the book, their Eugenics genes meant accelerated growth in their teens, but there was a "throwback" effect that made all the children be blond/blue-eyed.