A critique of technology lies at the heart of "The Veldt," and that critique rests on the premise that the promises of technolgy are deceptive. Technology, in a word, lies to us.
The Hadleys buy the HappyLife home because it promises them the good life: the house will do everything for them. It rocks them to sleep and raises their children. But the Hadley parents soon find that this idea of the good life is a lie: the house has robbed them of actually living their lives: Lydia Hadley, in particular, feels empty and useless.
While the parents begin to understand that the easy life technology offers is far more nightmare than sweet dream, their children, Peter and Wendy, are completely seduced by the technological wonders of their nursery. The viewscreen has become their true parent and through its endless repetition of scenes of the "survival of the fittest" on the veldt, brainwashes the children into its own lack of morality. Survival is its creed, and the children quickly begin lie to help this "parent" survive. When the parents reveal they are worried about what the children are watching in the nursery, the children change the viewscreen to pretty pictures when the parents enter, though the smell of blood from the veldt is still in the air. At the end, the children lie to lure the parents to the nursery, slamming the door and locking them in to be devoured by lions.
Bradbury's message appears to be that we must do the hard, honest work of living life or technology will devour us.