We also know that time passes at the same rate in both worlds. When Mike and Sulley are banished, they have to trek down the Himalayas, and when they get back to their world, time has advanced. So one minute in our world is one minute in the monster world, and we don't care how much fanfiction you throw at us that says otherwise.
With that in mind, the cute, whimsical Monsters, Inc. is the worst possible nightmare for the parents of Boo, the little girl who enters the monster world. She arrives at the end of Sulley's shift, which is dawn on Earth. Imagine her parents waking up, going to check on their precious toddler ... and she's gone. Just gone. There are no signs of forced entry, no demands from a kidnapper. Police would have absolutely nothing to go on. If anything, they'd probably suspect Mom and Dad. The best theory anyone would be able to come up with would be an ultra-specific rapture.
And then, 12-24 hours later, she's back in bed. There's still no explanation or clues. She's babbling about a big furry monster and a giant eyeball, but she's too little to be coherent and no one would believe her anyway. She'd be national news. Conspiracy theories would abound, and the parents would be accused of faking the affair for attention while trying to deal with their very genuine trauma. No one would ever get closure, and Boo will have a weird life when she learns about all the fuss that was made over her. Imagine her at 45, still wondering if those bizarre faint memories are real or not. Monsters University better teach students the whole damn story as a cautionary tale.