The White Witch of Narnia was not the rightful Queen of Narnia. She knew of the prophecy:
When Adam's flesh and Adam's bone
Sits in Cair Paravel on throne,
The evil will be over and done.
In other words, humans (the children are sons and daughters of Adam and Eve, the first humans) are a threat to the witch. There are four thrones at Cair Paravel, and there are four children. As far as the White Witch is concerned, they must not be allowed to be kings and queens of Narnia, because then her own rule would be over.
The White Witch hates humans in Narnia because of a prophecy that says her power will be broken by a human. She seeks to dominate and control all life in Narnia by keeping humans under her thumb through fear and manipulation. By capturing them, she aims to eliminate any potential threats to her rule.
Because she knows the prophecy foretells her own destruction will come about when humans appear in Narnia agian.
She turned them into stone.
The White Witch ordered Maugrim to capture and kill any humans that entered Narnia, particularly the Pevensie children. She saw humans as a threat to her power and wanted them eliminated to maintain control over the land.
The White Witch in Narnia was watching for humans because of a prophecy that foretold that humans would play a role in ending her reign. She feared the arrival of the sons of Adam and daughters of Eve as they posed a threat to her power.
Tilda Swinton played the White Witch in "The Chronicles of Narnia" film series.
The creatures in Narnia felt nervous about humans because they had never been around them before. The Chronicles of Narnia fantasy novels were written by C.S. Lewis.
In the book "The Chronicles of Narnia," the witch is called the White Witch or Jadis. She is a powerful and malevolent sorceress who rules over Narnia with an iron fist before being ultimately defeated by Aslan and the Pevensie children.
Jadis of Charn, aka the White Witch.
Her name was Jadis the White Witch.
Aslan
Her name is Jadis, but is known to most as the White Witch.
In the Narnia movie series, the character of the White Witch, who is the antagonist and queen of Narnia, was played by Tilda Swinton in "The Lion, the Witch and the Wardrobe" (2005) and Jadis (the White Witch) in "The Chronicles of Narnia: The Magician's Nephew" (which hasn't been released yet).
Edmund initially betrays his siblings by telling the White Witch about them and their presence in Narnia, seeking to gain favor with her. This act of disloyalty and betrayal can be seen as Edmund's "crime" in the story.
The White Witch