Part of my job when I'm selling books is to issue the occasional warning. One category of those warnings is: the first chapter is tough, but stick with it. I say this almost every time someone says they're thinking of getting The Hobbit for their child. It's true, the beginning drags. But just stick with it, I say, until Bilbo hits the road. As soon as he gets moving, so does the plot. Another book which gets this warning is The Borrowers by Mary Norton, which was a big favorite of Mona's: little people living under the floorboards. After we read it the first time, she always refused to let us read the first chapter, which explained why the full-size human boy was living in his elderly relative's home, and had nothing to do with little people.
Scary, as you so eloquently put it, is a little more complicated. Each child -- and each parent -- reacts differently. The wonderful Santore-illustrated Wizard of Oz whose praises we've sung here -- is often rejected by parents because they think their children aren't ready for the scary parts. When I read it with my girls, I kept a post-it in the book reminding me of the three pages where I would skip a line or rework something scary: the one I remember is the decapitation of a cat, which takes place in half a sentence.
I've run into quite a large number of kids who can tolerate -- even enjoy -- scary stuff in the context of fantasy writing: as long as they know it's taking place in an imaginary world, it's okay. But they will reject books with real-life bad situations that they can imagine happening to them or those they love.
So much depends on what age a child is. The death of Babar's mother is often much harder on the parent who is reading than on the child who's listening and, like Eleanor, doesn't quite yet understand what death is. I have vivid memories of the specific moment at which each of our girls was devastated by realizing someone we were reading about was dead. In Lizzie's case, it was Andrew Jackson; for Mona is was Casey Jones. There was nothing exceptionally traumatic about these deaths over other ones that had come up in their books. The difference was their growing awareness. Both girls were around 5 or 6, and had matured to the point of understanding the finality of death.
Leaving scary for a moment, the other place it's clear that kids reach different levels of understanding at different ages is sense of humor. A wonderful school librarian I used to work with told me she never recommended The Phantom Tollbooth -- which is full of wordplay -- before the third grade. Second graders, she said, can sit and listen to it straight-faced. But try reading it to the next grade up, and it's hilarious.
You ask about when is the right time to introduce your child to books with scary bits -- but there is no clear answer. It sounds like Eleanor is figuring out how to handle scary stuff -- and that she likes it enough not to reject it. I think parental comfort with the level of scary is equally as important as the child's. Stopping and talking about something scary can help. A friend's child would simply reach out and shut a book his mother was reading if it got too creepy: a clear message.
I'm going to leave fairy tales for another post -- lots to explore there in the wonderful world of the subconscious.