I might not have read enough comics about Lex Luthor yet, but I think this is the big difference between Lex and Doctor Sivana. The latter has no problem ordering a kid to be killed, while Lex would have found a way to use Captain Marvel’s secret identity to his advantage. The way I see it playing out is Lex trying to mentor young Billy Batson and influencing him to use his Captain Marvel powers. Or at the very least, blackmail him or use his resources to take him out of the picture without killing him. While I think Lex Luthor is evil, killing a child seems beneath him.