First, apologies to Martin for the sarcasm above. He and I got off on the wrong foot many months ago, because I thought he was just a lazy college student who was asking people to translate textbook exercises for him. But after reading some of his recent posts about verse-translations, I think he's a sincere learner of Russian -- although he should proofread his own posts better! (I was sarcastic above because the text contained some extremely elementary grammar errors (Лизавета дал ребёнок instead of Лизавета дала ребёнка) and obvious typos (мопоко instead of молоко).

But anyway, if I correctly understand the storyline of Иван и Лизавета, it seems to me there is supposed to be an element of sexual perversity in the fact that Lizaveta allows Boris to drink her breast-milk, since Boris is a grown man and a murderer!

So, for this reason, maybe it would be better to say Она дала Борису сосать грудь; он кормился молоком; оно было сладким на вкус ("She let Boris suck her breast; he fed on the milk; it was sweet to the taste") or something like that? (Instead of Она стала кормить Бориса грудным молоком, "She began feeding Boris with breast-milk").

I mean, the phrase дать сосать (literally, "give to suck") can definitely have a sexual meaning, assuming that's what's required in the context of the story.

Or, one could directly translate Martin's English phrase "suck the milk from her breasts" with the verb высасывать/высосать, which means "to suck something (liquid or air) out of something else".

Thus, if I'm not mistaken, one can say "Вампир сосёт мою шею" ("The vampire is sucking my neck") BUT "Вампир высасывает мою кровь ("The vampire is sucking-out my blood").

So, Martin, you need to decide as an author whether you want to more strongly emphasize the maternal "nourishing" aspect (кормление) or the sexual "sucking" aspect (сосание), since that would affect the Russian translation.