I would say that this belief is utterly absurd, but since there is a shred of historical truth to it, it can’t be entirely dismissed. That said, among modern Pagans, these things would be completely unthinkable. While there are some faiths that still perform animal sacrifices, you’d be hard-pressed to find many instances of it in modern Paganism. As for babies or children, I’m not sure there’s any proof that such things were ever practiced. They certainly wouldn’t be today.
As a religion that holds nature in the highest regard and considers life sacred, the idea of killing something for magical purposes is counter-intuitive. If anything, a personal sacrifice would be more likely, and even those, in a sense of harming oneself, would be quite rare. There is evidence that animal sacrifices were used in the far past, but modern Paganism frowns on this practice more often than not.
Simply put, you’re not going to find modern Pagans engaging in the killing of other beings for anything other than necessity, such as to provide food. One might use inedible parts of a hunted animal in a spiritual working, but they’re not going out murdering bunnies and babies to spill their blood upon the altar.
*Disclaimer: I no longer practice Paganism, but I’ve left these Pagan Myths articles active because I believe they’re still valuable in helping people to understand Paganism and reduce negative stereotypes.*