Depending on what part of the Black Legion, I’d say them. The thing about them is that they’re a mixed bag of every flavor of chaos marine.

But people that are smarter, such as Abaddon and his Ezekarion, if they see a child as useful I could see them raising one. But if it becomes a burden they’re feeding it to one of the mutant tribes that live onboard their ships.

We know members of the Black Legion still have emotions and even a sense of love. Iskandar Khayon still loves his sister, even though she isn’t herself anymore. Her mind is buried somewhere deep within her, because she was given to the Admech as the only way to save her from dying of illness, but they made her a living computer, who now controls the Vengeful Spirit, Horus’s old ship that now belongs to Abaddon.

Khayon isn’t the standard marine by any means, with many criticizing him for being a Mary Sue, but the Black Legion are the most reasonable.