Preface the announcement by saying "I love you," which will put your child at ease as they listen to you explain how love can crumble at any moment.
Begin with a simple, straightforward explanation of why this divorce is happening, what it will involve, and who Susan from marketing is.
Don't resort to the blame game in explaining why you're separating, as the kids will handle that part themselves.
Explain that divorce is actually fairly common. Your child might find it comforting to know that many of their classmates find themselves in the exact same hellish dungeon of pain, rage, and bitter, unending sorrow.
One easy way to expedite this whole thorny process is to tell one child and let word spread on its own.
Be patient, listen as much as you speak, and display other empathetic qualities that your marriage failed to incorporate.
Assuage your child's concerns by reminding them that only a small percentage of kids from broken homes become murderers.
Remind your kids that while it may be difficult now, things will get easier with each subsequent divorce.
No matter how you decide to explain the situation to your child, the most important thing is to do so better than your spouse.