That's amazing. I was reading the newspaper at seven or so, my parents got the morning and evening papers, and I wasn't an especially good student either. By the time I was ten or eleven I was reading adult novels from the library, though I was eleven in 1967, so novels were a lot different back then. Not so much mind candy. I distinctly remember reading my first Fletcher Knebel novel in the fifth grade, because I remember asking my teacher about some aspect of it.
Of course, I see you're from Nova Scotia, a place I have no familiarity with, and perhaps retaining one's innocence longer there is more normal than in a major US city, where I grew up. I was also assuming that this generation of pre-teens is more worldly than I was in the 1960s; they seem that way to me. It's also possible that I erred the other way with my own children, trying to grow them up too fast.
You're just special, that's all.
I was three in 1967, so I'm not that far behind you. I read voraciously as a kid, including my dad's subscription newsmagazines (we lived too far out in the boonies to get newspapers). And, I watched the news, including reports from the Viet Nam War. Unpleasant news didn't really bother me. I guess it was just too foreign or abstract for it to hit home and bother me, at that age. I can't remember when I found out there was no Santa Claus, but I think it was more of a drawn out process than a sudden bombshell. More like an inkling, turning to suspicion, to firm realization.
My daughter certainly isn't "slow". She actually reads voraciously - it's just "age-appropriate" books that she reads. She's gradually getting into more advanced reading and has read the "Anne of Green Gables" series, which has some sad parts to them.
She brought home a book recently from her school library - the diary of a young Irish girl emmigrating to America during the 1840's. I had an inner "uh-oh, this might not be good" when I saw it. But, I didn't say anything and she started reading it. Well, that night she she started bawling in bed about the horrible things this girl went through. You can probably guess how it went: famine causes widespread starvation/death, her mother dies of typhoid fever on the voyage across the Atlantic, etc, etc. It was a hint of how difficult life can be and I think she's starting to come out of that bubble. Her pet hamster and her great, great aunt also died this past summer, which put the issue of life and death front and centre for her. I don't see any reason to completely deflate any residual inflation from her bubble right now, by telling her there's no Santa.
All kids are different and we can't just treat them in cookie-cutter fashion.