Why was Peter screaming, “Don"t let father kill everything”?
Peter's petulant outburst is in response to his father George's long-overdue decision to close down the nursery in their automated home. George and his wife, Lydia, have become increasingly concerned at the way in which the nursery has become a technological Frankenstein's monster, taking on a life of its own as it effectively turns Peter and his sister, Wendy, against their parents.
The nursery was supposed to keep the children occupied and to stimulate their imaginations—not to cause them to hate their parents. Thanks to the long hours they've spent in the nursery, Wendy and Peter have become completely separated from real life. Instead, they inhabit a fantasy world red in tooth and claw, based on nature in the raw.
As this is now the only kind of life they know, they see George's actions in closing down the nursery as not just being unfair, but almost as an act of murder. As far as the children are concerned, George is "killing everything"—killing all the wild animals of the veldt with which they've established such a close and deadly bond. When Peter lets out his plaintive scream, he's calling directly on the ultra-realistic wild animals that prowl around the nursery to stop his father from "killing" them and their environment. And, of course, the only way that the animals can stop George in his tracks is by killing him. So Peter, in effect, is calling for the animals to kill his father—which they obligingly do.
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