In CoK they did reference Craster sacrificing his sons to "his gods" but they treated it as his term for a pragmatic expedient of offloading mouths to feed/competition for breeding. After the massacre at his keep, a comment by one of the wives reveals to the readers that his practice is not just superstition, but that his offerings DO keep the Others away as he claimed, for the simple reason that he is apparently augmenting their population.

That always sticks in my mind, because that was what got me to notice that a lot of the pragmatic politics everyone lauds about the series is really bullshit. Initially Jon complains to Mormont about associating with someone as degenerate as Craster, and Mormont downplays their relationship and points out that good terms with Craster has meant safety and shelter for rangers in the past. Well, now it is revealed that for those nights spent beside a fire and those gruding meals, the Night's Watch has allowed the protection and augmentation of their real enemy, the one they were created to fight! Jon was RIGHT when he cited those stuffy old honorable Stark morals. While those morals might look like weakness to the Greyjoys, Boltons and Baelishs of the world, Ned & Robb were only made vulnerable to those enemies by their own failures to live up to the code of honor, and the extent to which they adhered to their honor means that people like the Manderleys, the Glovers, the Mormonts and the clans are ready to fight for their children and avenge their betrayals, and even Stannis is not without sympathies for them. This notion is my equivalent of Egwene for the series, and the spark that got it going was the realization about Craster.