Final answer:
The psychologist couldn't take his eyes off of the children because of their dangerous obsession with the nursery's virtual reality simulation of the African veldt.
Step-by-step explanation:
In the story, 'The Veldt', the psychologist couldn't take his eyes off of the children because he realized that the children had become completely absorbed in the nursery's virtual reality simulation of the African veldt. The nursery was designed to create a personalized fantasy for the children, but it had become a dangerous and unhealthy obsession. The psychologist was concerned about the negative effects this obsession was having on the children's emotional well-being.