That doesn't mean vampires attack children. But the blood of children is supposedly supposed to be more delicious than that of adults. Probably because children are generally very innocent.
Vampires can taste the feelings and memories in another person's blood. Perhaps with children, because their world is still so white still. I don't know. The only blood I've tasted belongs to Kaname-senpai. And Aidou-senpai once for survival.