Boo is restrained and the scream extractor is moving forward to her as she screams until Sulley saves her.
At the beginning of the movie (after the opening credits), a monster slowly stands up beside a bed with a kid sleeping on it, and the score gets pretty scary. The boy turns and sits up and screams, but the monster immediately screams louder and slips on a soccer ball/football and some jacks. In other words, what looks like is the scene about to turn pretty scary actually ends up being funny.
Mike is restrained and the scream extractor to confess were Boo is at, and as the extractor is moving forward to him as he screams until Sulley disconnects the extractor. And when it's connected again by Randall, the one who is screaming in the extractor is Fungus.
There is one scene where Mike takes away Boo's bear and she cries loudly about it.
Pretty mild-mannered/lighthearted movie.
The screams from kids in their bedrooms while on the Scare Floor may frighten the younger kids watching it.
Boo's screams and laughter combined causes all the lights in the entire apartment complex to light up and cause a power outage.
During the opening credits, the closet that becomes an open doorway from the Monster World with a gigantic monster roaring can be frightening to some younger viewers.
None/Mild for neurodivergent viewers.
Sulley does a really big, scary growl for a demonstration and frightens Boo who runs away in tears (we see images of his face later, with teeth and claws bared).
Sulley thinks Boo has been smashed in a compactor and he faints from despair.