They are children of Dracula and his Vampire Brides. As vampires are the undead, their children are born dead, and all the babies seen in the film are hanging motionlessly in their cocoons at the starting point. They can be brought to life, or unlife, by the energy extracted from strong creatures like werewolves, but the only attempt at this failed when the werewolf gave out, killing the babies permanently. Another way of giving them life is using the energy of Frankenstein's Monster, and this might have given them permanent life if Dracula had not been killed.
Vampire babies come in great clutches; a single bride may give birth to a thousand or more in one go.
The babies are white like the brides, with heads roughly resembling those of vampire bats. They cannot speak and communicate using screeches and hisses. They are small enough to rest on a human shoulder, but strong enough to haul people into the air when teaming up with one or two siblings.(Are very cute in my opinion.):)