In Vampire Knight, Yuki's parents had a son that they named Kaname, but that child was sacrificed by his uncle to resurrect the progenitor of the Kurans who was also named Kaname. This progenitor had to revert to the form of an infant and was taken in by Yuki's parents. At any point did they realize that this wasn't really their son?
I think they did. Just like the person said above, Juri said that her son was already taken away from her. Maybe this was referring to something else but I don't think so.