This began as a reply to Morton Gray's comment. But then there were too many links to include in a comment. And once I get started talking about kids' books, I do get a bit long winded. I had the same troubles for many years. Patience was a precocious reader, but at eight years old found even Nancy Drew books too intense. In her defense, we had a Nancy Drew computer game. Prudence was bad at it and I was worse. Poor Nancy routinely died from our bad choices. Patience had good reason to worry over Nancy.
I found some of the most satisfying books for the kids at that age were some of the older titles. They have a complexity of language and story that is satisfying, while skirting some of the darker bits. Swallows and Amazons never caught with my kids, but is often recommended. The Eager books however were much loved at our house. There are Mr Pooper's Penguins which is a new movie and other award winning books. Andrew Clements books are amusing and fun but still hold a place in my kids' bookshelves.
As he gets a bit older, there are some more modern books as well that appeal because of the interesting content, even after the reading level is a bit unchallenging, but still have that reassuring feeling that nothing bad would happen.
Anyone have anything else to recommend to a young reader who doesn't want to read anything too dark?