Why did the Hadleys originally purchase the nursery?

In Ray Bradbury's "The Veldt," The Hadleys (George and Lydia) originally purchased the nursery to serve as a healthy outlet for their children's anxieties and frustrations. The nursery is basically a virtual reality room, one that can manufacture virtual landscapes to match what the children (Peter and Wendy) conceive in their minds.
However, the nursery eventually becomes an obsession for the children, and the Hadleys decide to "kill" it. Just after George flips the kill switch, Peter and Wendy begin to wail loudly. They throw a terrible tantrum, and their behavior prompts Lydia to ask her husband for a reprieve. Reluctantly, George agrees and turns on the nursery.
He tells the children that they can only enjoy a few moments in it, as he is taking everyone on a much needed vacation away from the house. Peter and Wendy sequester themselves in the nursery while George and Lydia go to their bedroom to get ready for their trip. Eventually, they hear the children calling them; both parents run downstairs into the nursery.
The story ends on an ominous note. Having locked their parents up in the nursery, the children sit down to enjoy a picnic lunch. The text implies that the lions in the nursery  devoured the parents, but the children seem unconcerned about their deaths.