Visible crew/equipment: As Nell runs away and tries to hide in the carousel for the second time, the camera, in an above shot, passes behind a pillar. Just after that we see the reflection of a camera's tripod in one of the glasses across the room on the right side of the screen. (01:14:50)
Visible crew/equipment: At the end of the film, when the Dudley's arrive, Mr. Dudley opens his door, and in the far right of the door window, a crewmembers head is reflected.
Visible crew/equipment: As Nell turns around to see all the lights in the house turning on, we see in the background, the rest of the group trying to save Luke, but at the very beginning of the shot, you see a blue light quickly flicker behind Nell, that couldn't have been the cars lights, which only means that was the crew's lights.
Visible crew/equipment: When the carpet pulls Luke along the floor, you can briefly see a wire pulling it.
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.