I would recommend a trial separation on a case by case basis; if people know that there is no possibility of saving their marriage, then there may not be a reason to have a trial separation. If you are going to have one, I would definitely sit down and talk to your children about what is going on, they need to know before all of a sudden one parent disappears to another residence, I think it's very important that they realize that they are part of the process and whether it's a trial separation or an actual separation, I think you have to be united front when you talk to your kids and you really need to be able to explain to them that, although they are part of this family unit, the reason for this separation does not have to do with them. Some kids personalize it : "It's my fault, it's because I did this" and depending on their ages, they will react differently. "Mom and Dad still absolutely love you, we are still a family, we are still in this together, that's why we are talking to you together, but we want to make some changes in the way we live that will hopefully make us all get along better and have a better family life". And I would definitely recommend speaking with some kind of mental health care professional that specializes in children and your aged children and in break ups that can really help, guide you through that conversation.