It is important not to discuss divorce plans with children until the ultimate decision is reached. This means the break-up of their family and is usually a very difficult time.
The news should be broken with BOTH parents present. The news should occur a few weeks before the separation if possible so there is some advance warning.
Parents should break the news without blame or accusations about each other.
A family meeting, ideally should be called. This helps the children gain closeness with one another and conveys the parents' willingness and availability to discuss further separation and divorce issues. If the discussions with children are separate, there develops an air of secrecy and distrust toward parents. It is good to let children know about your feelings of sadness in moderation or of anger.
Discussing the reasons for separation opens communication and trust between parents and children and educates children about the reasons for the discord.
In fact, marriage is a skill set. It is important to explain to children what went wrong, in age-appropriate language rather than to say, "we don't love each other anymore." The latter leads children to become adults who believe that if they stop loving, they should leave. It makes marriage about romance and not about commitment.
The children should know that they were products of love and that you wanted them and expected to be living together.
This enhances the children's feelings of self-worth. Explain your regrets and the reasons for leaving. If infidelity is an issue, as it often is, let the partner who stepped outside of the marriage speak for him or herself. It would be hoped but is not always the case, that that partner can comment on the betrayals and breaks in trust as a result, and apologize.
If the partner who feels offended begins to criticize the other partner, it makes the children feel badly and also they become caught in the middle between the two warring partners.
The children need to know that they are loved and the divorce is not their fault. They need to know where they will live and how their lives will look after the divorce. They also need to know if finances are changing, that they will have what they need even if things are a little tighter. They need whatever updates are necessary about the facts around where they will live, visitation, and so on as this helps to control the anxiety that comes with the uncertainty of change.