When George and Lydia Hadley consult with a psychologist, David McClean, McClean informs them that this technology could be employed to gain insight into the psychology of the children who use it. In this case, McClean is disturbed by what he has observed.
As David puts it, George and Lydia have been replaced by the nursery, which has taken on a parental role in their children's lives. Furthermore, by threatening to withhold access to the nursery as a disciplinary action, the parents have actually become subjects of hatred for their children. Thus, the entire relationship between parent and child has been poisoned by their reliance on the nursery to such a point that it necessitates immediate action.
For this reason, David suggests they immediately shut down the nursery and make sure that the children begin receiving psychological help so as to prevent the situation from deteriorating any further. While he recognizes that this will be a difficult adjustment to make, he is convinced that, by removing the technology altogether from their lives, they would give themselves the best option for repairing the damage that's been done.
The parents decide to accept this advice, but in the process they raise their children's ire. The consequences are fatal as the story concludes.