Parents should know that the firefighters in this show are very human and the situations they face are ones that can affect everyone. Although the are unflinching in their word choices and their dependence on alcohol and drugs and sex they are a team who are devoted to each other. They tend to have very frank discussions regarding their sex lifes and frequent arguements erupt between the characters. They all seem to suffer from PTSD as a result of 9/11. Tommy, the main character, seems to have the most issues and several times over the series he is faced with an unimaginable tragedy. He relies on alcohol throughout most of it and very rarely deals with his issues and showing emotion. There are many adult themes that the show deals with including, but not limited to suicide, alcholism, drug addictions, depression, adultery, divorce, murder etc.
These things along with the characters reactions to their personal issues, especially 9/11, can be discussed with kids.