Heck, even the lobby is scary enough for someone who doesn't want to ride it so I doubt this is true.
Funny story with my father-in-law. We knew he would NOT like Twilight Zone but he was interested in seeing the Rod Serling stuff since he remembered the Twilight Zone series when it was the real TV. Since we had been on the attraction many times, we assured him he could just simply go through everything with us and then he would be escorted out before the plunge (I had done that earlier and knew he would be fine). While walking through the lobby, he started to frown, then the library. He loudly asked if this was "THE DROP!!!!!!" we explained that it was Rod Serling and I started to worry. But, he was OK as we made sure he was back up and far away from the TV and he was supported by a wall. We stood in front of him and he held onto my shoulder the entire time (because I had taken the alternative exit earlier so he thought I knew was I was doing for him). My shoulder hurt for quite some time

. And then we went to the boiler room. We waited until everyone else exited the library and talked to him and told him he would be fine. Er, no. He kept asking me, all through the boiler room when he was going to get out. When was he going to get out?! WHEN was HE going to get OUT?! Once at the seater person, I explained that he wanted to leave and when the Cast Member had to hesitate to get others into the boarding area, I remained with my father-in-law until he could be escorted out.
Once the rest of us plunged, we met my father-in-law at the end and he was all smiles and having a pleasant conversation with the Cast Member at the photo area. Although he told us that he would never do ANY of that again because it was too scary for him. I bought him a pin after and he laughed.
So no, I don't think Disney would make a child wait in the library at all. My father-in-law was in perfect health and was a psychiatrist and let us know later the triggers that Disney caused his fears to come out.