This is such a ridiculous question. Yes, children complicate the situation if a couple find that they no longer want to be married, but staying together just for the sake of the children will not solve their problems- in fact it will just exacerbate matters. As a person whose parents separated when I was 9, I can honestly say that as difficult as it was initially to deal with, it's not the end of the world. And I would much rather know that my parents are both happier now that they've moved on, than having to feel guilty that they stayed together so as not to upset me- and were miserable themselves.
Couples who do not want to be together should not stay together just for the children. Because, guess what? Children pick up on their parents trouble, and it worries them. I had parents who tried to stay together for my benefit, and all I did the entire time was worry about them both.
While kids should ideally grow up in a home with two parents, sometimes it's better for kids to grow up in a single-parent home rather than growing up in a home with two parents who are fighting all the time. Children cannot thrive in a hostile environment like that, so their parents should be allowed to get divorced.
Divorce, like marriage, should be granted to any consenting adult in a country that puts no legal restraint on the reason for it. The presence of children not only complicates divorce, but does have lasting psychological damage on them; for this reason divorce should be avoided, but not outlawed or forbidden. Oftentimes a couple that is willing to divorce do not have the coping skills to remain a married unit and need to either receive personal or group counseling before continuing to function as a unit. While I do agree that couples' therapy should be mandatory for those seeking a divorce, there are instances where counseling, therapy, and even significant changes in the significant other will not make the marriage work. Children are humans growing up in an already difficult world, but the concept of divorce is not a world-ending one and many children that are given proper coping skills throughout divorce and are given proper care from both parents and other people in their communities are just as capable, if not a little more so, at handling emotionally charged situations as their peers who have had a 'charmed life' by comparison. In the end, banning divorce because of the presence of children makes as much sense as banning bankruptcy because of the presence of unused, unsold, or outdated chattel.
A free society should not even contemplate keeping people locked into a marriage they wish to dissolve. The implication that such would be better for children is erroneous in any case. Yes, children are better off with two parents in a stable relationship. But parents that want to divorce will not provide a stable environment even if forced to remain together. It will likely be acrimonious and even worse for children than the alternative.
Couples with kids should be allowed to divorce because parents with children out of wedlock are not forced to get married. People should not be forced to get or stay married simply because they have children. Studies show that keeping children around a dysfunctional home can be more detrimental than divorce.