Trivia: Ridiculously huge Jesus reference at the end. When Eleanor is blasted onto the door, her arms and legs are in the same position Jesus would've had. She is lowered down by the hands, much like Jesus would've. She also dies to save everyone else, a slightly smaller point is that you see the children 'die' and going into heaven. The bible says 'only those who are like a child are to go to heaven.'
Trivia: When Eleanor is in her bedroom, look in the mirror: both times you see children heads or portraits.
Answer: Another possibility is the spirits of the children. As long as Hugh Crain was inside the house, the children were trapped inside too. They could have called Nell because they needed her help in being set free.