Most organizations have policies that may, I stress may, apply here.
First, when you say "offensive comments", do you mean profanity or threats?
If they are using profanity in the workplace, Management and HR might be interested and want to put a stop to that. Now, with that said, every office is different, and if a person let's a few profane words slip out now and again, it might not be enough to warrant any sort of intervention. You should really consider what are the normative behaviors. In other words, is what these people say within the norms of your workplace? If yes, then move along on this point.
Threats can be analogous to profanity in that they are something no one wants to hear, but in the course of day to day language they are much more acceptable than even profanity.
"I could kill my dry cleaner. He ruined another suit."
"This idiot driving in the slow lane today should be shot, and I'm willing to do it."
"For all the money my wife spends on clothes, I should divorce her. No kill her first, then divorce her."
People have these sorts of outbursts that can be very commonplace. Once again, if what the people in question are saying fits within workplace norms, move along.
A second line of thought is whether the offensive comments are creating an undue workplace interruption for you. If so, then both Management and HR are more likely to take an interest because that impacts the bottomline if the work isn't getting done. As with profanity and threats, you must consider whether the behavior fits within workplace norms. Do they talk about their rotten kids for a few minutes at a time a few days out of the month at their workspace? Do they talk about their rotten kids for two to four hours at a time each and every day at their workspace? In between these two extremes lies the reality. If it's closer to the former, move along. If it's closer to the latter, then you definitely need to raise it up to Management and HR under the context of workplace interruption.