How does the setting in The Veldt fit the description of dystopian?
When it came to the intersections of technology, convenience, and entertainment, Bradbury was often rather ambivalent. This can be seen in many of his stories, most notably Fahrenheit 451, in which reality television has largely taken the place of reading, talking, and critical thinking. From Bradbury's perspective, technology wasn't entirely without value, but it had the strong potential to replace the human connections that develop around engaging with others through discussion and interaction.
In The Veldt, the concept of simulated engagement takes the form the nursery, which the parents use to occupy the children. Rather than spend time with their children and develop a bond, they are relying on technology and other modern conveniences to raise them. They're inability to bond with the children, who subsequently bond with the nursery, is ultimately their undoing, as the nursery is eventually used to kill the parents.
Throughout the story, modern convenience - particularly the nursery - symbolizes the dystopian future that Bradbury believed was possible. The family assumes that all the technology has made their lives easier and happier, but in the end it has mostly served to disconnect them from each other, which is why the children are easily capable of orchestrating the murder of their parents.