Key Takeaway

Make it clear that it's not their fault, they will be taken care of, and you will always love them. Avoid blaming the other parent.
Many kids feel guilty and that they did something to cause the break-up. Emphasize they are not the reason for their parents splitting up. Kids do not cause separation or divorce. It is not their fault.
Emphasize their support network. You can also try to normalize their experience and let them know that lots of kids go through this. They probably know some kids with separated parents.
Reassure them you will continue to love and care for them.
Prepare them for changes ahead. Reassure them without providing unrealistic promises.
Recognize that emotions such as sadness, anger, confusion, and guilt are normal. See Identifying Feelings for advice on coping with emotions and how to create a feelings friendly environment.
Sometimes it's hard to find the right words, here are some ideas of things to say to your children to reassure them.
This places blame on one parent and can make the child feel responsible or conflicted. "We're getting divorced because your mom/dad is impossible to live with. It's their fault."
Providing inappropriate details can burden children with adult issues and create confusion. "We're divorcing because your dad/mom cheated on me, and it's a big mess."
Keep discussions about moving, changing schools, lifestyle changes, etc. for another time. Older children may bring these points up, but if these decisions have not yet been made, only speak about them in general terms. “We are breaking up. We are probably moving and you are going to be changing schools, and…”
They will need support from their friends and extended family. If you are not ready for others outside the immediate family to know, then this is not the time to tell the children either.
"Don't worry; everything will be the same. You'll see both of us whenever you want."
False promises can lead to disappointment when reality sets in, causing trust issues. It is very common for children to hope that their parents will get back together. In reality, this rarely happens.
You need to be very clear with your children that the decision to separate or divorce has been made, and you will not be getting back together. False hope could prolong their adjustment period. Some children and teens also believe that if they behave perfectly and take on extra responsibilities, their parents will reconcile. Make sure your children understand that just as they did not cause the divorce, there is nothing they can do to change it.