Hi, I am guessing you are asking how to comfort a child after the parents have broke up. You didn't give much detail so this can be a little hard but if this is for a child then the best thing you can do is just show the child that both parents still love them and that has not changed. In a parent break up most children feel it's their fault and as a parent it our job to make sure they know that it isn't. Make sure the child still spends time with each parents and both let the child know that things are going be ok. Things will be different but they will also be the same. It's best not to fight in front of the child, don't talk bad about the other in front of the child, just try to keep things a calm and normal as possible. Most of it is just showing the child that they are still loved and that things will not be bad just a new start in another direction.
I hope I helped and if this was not what you were asking please let me know I will do my best to help.