Disney/Pixar probably are just emulating European classical storytelling that we find in fairy stories?
When you see the child in absolute terror, ask yourself "is this the right way to entertain a child, through pure terror?"
Or do the same thing with the Pixar movie "Up", a fabulous and gentle movie until it gets the mandatory part where they go all out to scare the living shit out of the kids watching with attack dogs.
Hansel and Gretel are a young brother and sister kidnapped by a cannibalistic witch living deep in the forest in a house constructed of cake and confectionery. The two children save their lives by outwitting her.
I don't think I was older than 5 when it's been first read to me.
One might think that one is an exception rather than the norm, so here's the beginning of another one[1] (more a ballad than a fairly tale, but no one would think it's weird if an 8 years old read it).
A king is hunting in a forest and encounters a house. He asks for water and a beautiful girl opens the door. He asks to marry her, but she says she needs to ask the step mother, who's in town at the moment.
The king returns later, asks the step mother, she offers him her own daughter, but the king orders her to bring the step daughter to the castle the next day.
The next day the step mother and her daughter take the step daughter to the forest, where they kill her, take out her eyes, and cut off her limbs.
The daughter then impersonates the step daughter and marries the king.
And so on. It ends relatively "well", with the step daughter being brought to life again, and the murderers "blinded, their limbs cut off and thrown to the wolves".
When the tales are adapted for the kids, the violent themes are often tempered down. The story themselves are often changed. Just visit a book store to see the numerous adaptations are 'Little Red Riding Hood'.
Also, for young kids, the book is filtered through the interpretation of parents. So they can mellow down certain parts based on their kid's sensitivities. Also, in books, the really gory parts are often left to the imagination and not every scene is pictorially represented. Fortunately or unfortunately, each and every fact has to be shown in some form in the movie. Movies tend to be more visually stimulating than books and tend to pull in the kids more.
On the other hand, books have the luxury of being able to provide stories tailored to each age group. Movies have no such luxury if they are to be financially viable.
Also each movie wants to have a villain more scarier than all the ones before and visuals (earthquakes, huge torrents of water anyone) much grander. You invariably endup with something frightening for kids.
But above all, kids' imagination are more volatile and fertile than ours. Their view of the world is incomplete and hence their interpretations of the same scenes could be radically different and unpredictable. Case in point, My four-year-old was frightened of 'My Neighbour Totoro', especially, the scene of Totoro on the tree at night and the catbus :) .
Maybe instead of reaching all kinds of dubious conclusions based on anecdotal evidence on how children look like during certain parts of the movie, you should instead ask the child, after the movie is over, whether he liked it or not. I think you will find that the vast majority of children greatly enjoy most Pixar movies.
The claim that Pixar movies, or the levels of violence depicted in them, are harmful to children or to society, has zero evidence in support of it.