What do you tell the children? I guess it depends a lot on their age and maturity level. I didn't want to tell her ugly things to make her upset. After all, it was HER dad.
 
Kids love their parents no matter what. How did I tell her about her dad's cheating? Well, to be honest, she was not old enough to understand what infidelity was. I had to tell her that her dad and I were not getting along and had some differences, but up until this date, she did not know what cheating was or anything about it.

When they are grown up enough to understand, then you have to approach the subject carefully because they do not want to believe the worst in their other parent. I wanted my daughter to still love her dad, even though he not only cheated on me, but on "our" family happiness.
 
Be gentle in your words. Explain things in a way that they might be able to understand, and make sure they know that it's nothing that "THEY" did. Although my daughter is a young teen, and understands more of what happened, she now knows that what he did was wrong, but she still loves him and wants him in her life. I, too, want him involved with our daughter.
 
I understand this oh so well, having gone through my own parent's divorce while being young. No matter how upset or mad you are, please be gentle with your explaining to your children. Keep your grown up problems to yourselves. Children are precious and innocent and deserve to believe the best in both of their parents.