I have had this with DD (5) who asked me in a very busy checkout queue at tescos what rape meant as she had read the newspaper headline by the till.
I do tend to keep my books separate from the kids books (just habit no real reason, I have done it since they were babies) and just make sure she has loads of different books to read on "her" bookcase.
Hi I'm having the same problem with my 5 year old DS. He asks a lot of questions that I struggle to answer. He is also a worrier so I spend a lot of time reassuring him about things, eg he was recently worried about catching Aids as he had read about it in a book. He also read a poster about domestic violence. It's difficult to escape them reading things so I just try to explain things as best I can while being sensitive to his age. He really enjoys News Round on CBBC and we try to watch it together so we can discuss anything he wants to know more about.
My 5 year old DS is a really keen reader. We struggle to find books with content suitable for his age at the right reading level but muddle through with a mix of Enid Blyton and non-fiction books (he loves anything scientific or mechanical).
The problem I'm having is that he's started to take our 'grown up' books down from the bookshelves, grab newspapers, magazines etc... and read them too. I don't want to have to hide all the non child-friendly printed material in the house but can't work out how to deal with it.
Also, it's not just at home. We had a problem a few weeks ago when he read a front page article about 'the death of Syria' while we were queueing at the checkout in the Supermarket - not least because my grasp of international current affairs leaves a lot to be desired.
Whenever we go out, I'm constantly scanning around me for things he might read that will freak him out/upset him.