This is a really hard question I think and we are facing it too. Older books don’t have the sex and mostly have less violence but they often have racism that is subtle. YA will often have a lot of sex and problematic vocabulary. I finally decided that I would tolerate the racism inherent in old adventures and sometimes I would have to accept sexual themes
I’m pretty sure my son’s first exposure to sex was Brave New World.
There are a lot of good books on the other thread. Nonfiction is often overlooked.
