The Unborn

Type: Revenant
The Order of Resurrectionists in the past have discovered, during botched attempts at resurrection, a phenomena where human souls return to the world of the living, but do not seem to posses any knowledge or experience, not even powers of speech and language.
It turns out they are the Unborn, the lost souls of children who died before their own birth. 
These Revenants posses the bodies of adult humans, but their minds are effectively undeveloped. They are children at heart and must be cared for and talk how to be human.