The toughest part of going through a divorce is helping your children throught it. Just imagine what little children feel when their parents break the news to them! They experience very disturbing feelings of guilt, hopelessness, insecurity, loss and pain. It is not easy to decide to leave your spouse, but at least you have a choice and a shared right to decide. But the children neither have any choice nor do they have a say in this big decision that is thrust upon them. This is why you need to be extremely thoughtful and loving when you break this sad news to them.
Even though you are breaking up, your children do not want to see you fighting. They need to see you being cordial and friendly with each other so that they know what to expect in the future.
Your children need to know that even though you are breaking up, you will still be a family and will always be there for them and for each other.
You have to reassure them that this is not the end of their relationship with either of you. You will both continue to spend a lot of time with them as before.
Whatever you do, do not get into the blame game. If you start pointing fingers, it will only add to their pain. More than anything, make sure they understand that they have no role in your breaking up.
Basically, you need to make this change as easy and non-upsetting as possible.