He's started so let him finish so long as he tells you if anything worries him.
Don't go too deep into explanations as it just confuses at that age.
I remember reading one of my dad's war stories when I was off school ill age nine (am sure of my age cos was ill on my birthday).
I looked up at my mother perplexed and asked "what does raped mean?"
Reply was " a man attacks a woman"
I spent the next couple of years convinced that, when I read about wife beaters in newspapers, these men were rapists.
Think I was like eleven and a half when understanding fully dawned.
As to bad language in books, just listen in to a bunch of kids when they think the adults are out of earshot! The swearing makes my teenage years in a coal mine seem like a bible class