Last year we had an issue with a story that our then 3rd grader wrote that was too violent for us as parents. While a little guidance at school could have helped redirect him, we learned more about how boys write and took a deep breath and backed off.
Here are some resources that have been helpful to us (and the kids).
My Weird Writing Tips by Dan Gutman (My Weirder School series author)
This fabulous infographic was in the New York Times Book Review over the summer