Again, an entertaining episode - the one about The Veld by Ray Bradbury. It's interesting how easily the thoughts about the 'mechanization and entertainization' of the house(hold) in the fifties (tv, vacuum cleaner...) and the worries and effects they could cause, can be translated in the modern discussions about the effects of the social media and digital world on our social system. But that's Bradbury. And I like his concern for children and parenting: a theme that's not often handled in literature, in my opinion (although there's Peter Pan and The Lord of the Flies...).
When I read this story, I also had this question in mind: was it a real lion that killed the parents? I also thought it strange if it was a real one (VR is not real). But if it was the girl, why didn't they see the girl? I think maybe the answer lies in the fact that this VR was induced by the mind, so maybe the images (and sounds and smells) are not received by the sense organs, but immediately by the brain itself. If that's the case, the girl could have 'disguised' herself as a lion, after messing around with the nursery-system (maybe a bit like 1 'if optical input=girl then optical output=lion'; 2. add lion to Veld).
But after all, I don't think the discussion about the lion/girl is not the most important one in this tale (although it's fun to think about) :-)
I had always assumed that the house (through error or tampering) was beginning to create corporeal lions, like tulpas, feeding off the aggressive energy and thoughts of the children. The technical "how" is not addressed by Bradbury, but he was never a "hard" science fiction writer. (Although it's interesting that Bradbury had a better track record than many of the hard sf writers in predicting technological and cultural change - just in Fahrenheit 451, he predicted walkman-like earbud music players, big screen TVs, what sounds a lot like MTV music videos, and the rise of political "cancel culture".) It's not often thought of as such, but "The Veldt" is a haunted house story for the technological age. If I were to edit an anthology of great haunted house stories, I would include it.
It was adapted, not too badly, as one of the episodes of Jack Smight's 1968 film "The Illustrated Man" with Rod Steiger and Claire Bloome.
My reading was that the lions had become, if not actually real, then able to interact with the real world in a way the designer of the nursery never intended (or did they?!). Even if Wendy killed the parents (which didn't occur to me until Brandon mentioned it, and I'm still not convinced), they seem to be able to eat things from the real world. At least if the implication of the final paragraph is that what the lions are "done feeding" on is the parents.
This story is all about human arrogance and hubris in the face of technology, and the deadly repercussions when that technology gets out of control. At first we assume the parents were foolish to run away from lions that couldn't have hurt them. But it turns out they were right to run. The lions are actually dangerous.
Bradbury is even explicit about this:
"“The lions look real, don’t they?” said George Hadley. I don’t suppose there’s any way —”
“What?”
“— That they could become real?”
“Not that I know.”
“Some flaw in the machinery, a tampering or something?”
“No.”"
Except there is, and for one of those reasons: there is either a flaw in the machinery or the children have tampered with it (or both). Personally, I favour the idea that the nursery has attained some level of self-awareness, because right after that exchange we get this:
"“I don’t imagine the room will like being turned off,” said the father.
“Nothing ever likes to die — even a room.”
“I wonder if it hates me for wanting to switch it off?”
...
They went to the fuse box together and threw the switch that killed the nursery."
To put it bluntly, they killed the nursery now it wants to kill them, either with or without the encouragement of the children. Although the fact that they also wish their parents were dead is certainly not a coincidence.
Brandon pretty thoroughly convinced me that it was Wendy who killed the parents, and I guess I've been envisioning that she was simply hiding in the shadows. But that's pretty simplistic because, of course, she had to somehow manage to kill two people without being hurt herself. I like your idea that the nursery itself aided her in this by playing tricks on her parents' minds.