What would be a good conclusion for an essay on "The Veldt"?
A good conclusion for any essay should involve a strong final statement that completes the narrative theme and train of thought that has been established by the author in the thesis statement. That thesis is, of course, up to the individual writer, but I think a fairly straightforward thesis for "The Veldt" might address the dangers posed by the rampant use of technology to supplement or replace human interactions.
While some advise restating the thesis in the conclusion, in practice I find this to be a bit pendantic and unnecessary. It is probably better to articulate a complete statement that summarizes and emphasizes the main points made in the essay, but does so in a way that was not possible at an earlier point, such as by citing evidence or building on previous statements. One might conclude an essay on "The Veldt" by stating that the lack of explanation for how and why the parents died in the nursery is entirely acceptable, and in fact necessary, because it builds upon and supports the unexpected nature of the relationship between the children and parents; danger sneaks up on us and our acceptance of the status quo blinds us to it.
A conclusion in response to a prompt such as this should also, at least in my opinion, make a claim for further action, such as by advising a means by which the writer's point can be fulfilled. For example, if we are arguing that technology when used to casual excess will reveal severely detrimental effects, we might suggest that exposure to virtual reality be restricted, perhaps by age or by the amount of time per day, in order to avoid the apparent confusion between reality and fantasy that the Hadley children experienced.