The most important thing in explaining your children about the divorce is that they are not the reason of it. Most of the children take blame on themselves and spend the rest of their lives miserably. They keep crying and cursing themselves and this spoils their future. Therefore, it is of utmost importance that you tell them they are not the reason and it is because the two of them. You should take them into confidence that you and your spouse have some disagreements and both of you cannot live together anymore.
To gain their confidence, you would have to tell them the reasons of divorce, which can be difficult for you. Some couples make the mistake of bringing third person into the matter and end up making things worse, you surely do not want to do that. Rather than taking help of the third person, you should convince your kid.
Having a divorce does not mean that neither of you will take the responsibility of the child. Note that, you should tell your child how important he/she is to you and the divorce will have no impact on your relationship with the kid.
Do not forget to take their suggestions and ask them if they want anything from you.
Allow them to ask you all the questions they desire and do not leave any question unaddressed.