Good morning. I am sorry to hear you are going through this difficult time, and obviously it is compounded by the need to explain things to your children. I actually went through this experience as a child, and have vivid memories of what not to do :)...perhaps these tips will help you and your spouse.
1--Your children are going to be upset, and they are going to have questions. Sit down with them with your spouse, even though that may be difficult due to tension between you guys, and explain things openly and honestly. Refrain from pointing fingers and placing blame on each other--it's not productive, and can be confusing. Answer all of your children's questions as best you are able.
2--Remain calm no matter how your children react to the news. Again, they are apt to be very angry and upset with you. This is natural.
3--They may leave the room, yell, or cry. Let them. Give them a breather if they need one. Then, both parents need to follow them and calm them.
4--Explain to them with as much detail as you are able about things such as how their lives are going to change. These are the things that are going to worry them--where they are going to go to school, where they're going to sleep, what kind of bedroom they're going to have, if their friends are going to be there, etc. Reassure them as much as possible. They will always, after all, have a place in your life.
5--Discuss plans for how they will see the parent they will no longer be living with full-time, or shared custody arrangements.
6--Reassure them --make certain they understand-- that this has nothing to do with them. Your love for them remains unaffected and unchanging.
Your reasons for the divorce have nothing to do with them. They did nothing wrong. These are all things that go through a child's mind when divorce comes up.
Aside from this conversation from the kids, some other things to keep in mind related to them:
I hope this has been helpful to you, johncal! Blessings to you and your family as you work through this difficult time.
Please let me know if there's anythings else I can do to assist.