It's not normal, but there have been times, throughout human history, when a young teenage girl was thought of as marriageable, and was often wed to a much older man. So, it's not unprecedented.
The goal is to keep kids innocent, while navigating and avoiding the open cesspools of sexual depravity easily stumbled upon via internet and the media.
I also, as a parent, cringed at some of the content that was discussed in literature and meetings, in regards to sex and destruction of society, via armageddon, and I remember as a child myself, being disturbed, really frightened, by the depictions of destruction. There are definitely things discussed on occasion, and things written about and depicted in the literature, that are not child appropriate. I mean, I wouldn't let my preteen children watch anything sexual or violent, so why would I want to let them sit and hear about it at the kingdom hall? And yet, I did, on occasion, and most witness parents did too... it's crazy how your belief and "faith" in god, will allow you to blindly listen to a religious organization, and shrug off any internal warnings, or gut checks, even when it comes to your children.