I beg you.
I plead with you.
Do not ever use your children as weapons.
Do not rationalize that they need to know the truth before their brains are even fully developed to cope with it.
They are half him and half you. When you demean him, you demean them.
Do not teach them hatred.
The best thing you can do for them is to make sure they love their father, not matter how you feel about him. They need your permission to love, to accept and to forgive. Do not abuse this influence that you have over them.