The Child of The Necromancer is a sort of Chosen One and alternates through the generations as sons or daughters. A son always succeeds a daughter and a daughter always succeeds a son.
They are the Voice of The Necromancer and their goal is to maintain the power base of this ancient evil and seek to set The Necromancer free.
The current Son of The Necromancer appears to have identified how to access the Tomb of The Necromancer via a portal from the mountaintop Temple of The Necromancer. He is a powerful spell caster who rides a magic carpet and wears armor.
The party has delayed attempts to set free The Necromancer.
The members of this cult are not afraid of death and willingly use undead to server their ends.
The party learned this from the lieutenant of the guards that they captured in the mountaintop battle. Hanagan the Red charmed him to get him to talk.