I don't have much doubt that Jews sacrificed Christian babies from time to time, and drained them of their blood. The historical and legal evidence is persuasive, if you actually take the time to study it. I doubt that it was done except in very unusual circumstances, as an avertive magical rite, to turn away some feared danger or threat. It was probably quite rare, and was probably a form of magic passed down within the Kabbalistic community of the rabbis, who were the possessors of the methods of Jewish magic.