I was both a precocious reader and a very sensitive child, and accordingly (and regrettably) read some books long before I was mature enough to properly process their contents. A few of the Sherlock Holmes stories terrified me as a fourth grader--"The Adventure of the Speckled Band" in particular--and James Michener's "Poland" gave me nightmares for weeks the following year. (Is there any piece of land other than present-day Israel where so much blood has been shed so cruelly for so many generations??)
Thing One is very much like I was in both respects, so we have to be careful what books we allow him to read at this stage of the game, especially inasmuch as he loves biographies. I don't remember how the topic of explorers came up, but Himself and I thought that the book "Endurance," the story of Ernest Shackleton's ill-fated 1914 Antarctic expedition and subsequent adventures on the way home, might be safe for him to read, given that everyone in the crew came back alive against impossible odds. He started reading that a few days ago.
Tonight, I was sitting in the kitchen going through my binder for tomorrow's Board of Ed meeting when I suddenly became aware of racking sobs coming from upstairs, where Thing One was reading before bed. I sprinted upstairs to find out what was going on, only to discover that he'd reached the part of the story where the starving men killed the expedition's dogs for food and was utterly distraught at the thought of having to take a knife to our beloved pet dog under any circumstances.
Parenting fail: we'd forgotten about that part of the story. Time to go back to the children's section of the library for bedtime reading material!