Your spouse cheated.  Or perhaps he or she walked out, ruining the life you had worked so hard to have for your family.  Now the whole Earth is tilted on its axis and the future holds uncertainty, a lifestyle far different from that which you have had for years, and being yet another "broken family."  Well, the kid should know whose fault it is that their world has been shattered, right?  They shouldn’t blame you, who had nothing to do with this catastrophe that has been inflicted on them, right?  
Wrong.  Don’t throw your spouse under the bus even if with every fiber of your being you want to.   All you children know is that they love both parents, and wish that you could get back together.  What your spouse did to you is not what he or she did to the kids.  And all that stuff that they say about daughters idolizing their fathers?  And son’s admiring their mothers?  Well, it’s not out there  for nothin’.  It’s true.  And study after study shows that children who grow up with a strong relationship with both parents, even in situations in which the parents are divorced or separated, grow up to be emotionally stronger and healthier parents themselves.  And you want that for your children.
As a young family lawyer, I was told that when there are children, a divorce doesn’t end a relationship.  It merely changes it.  And, in fact, when all the vitriol has died down; after the settlement has been reached, and each party settles down into their respective post divorce lives, they still have to co-parent together.   This is exponentially harder when there has been alienation of a child by one parent by the other.  It is even harder on the child who may have been alienated.  Be sure, if a judge finds alienation, even unintentional alienation, he or she will undoubtedly order some form of intensive reunification counseling.  Do you really want your child to spend twice a week with a counselor rather than out with his or her friends, on the soccer field, or on the beach?  They may resent you in the long run.
Divorce is hard.  It is even harder for the party who doesn’t want it, and who was not at “fault.”  But it is hardest on the kids.  They love you both and that will not change.