The divorce rate is rising with at least 45% of American marriages ending in divorce. What advice would you give to couples considering marriage? How would you explain the impact of divorce on children to these couples?

The difficult fact is that those who are in love are typically likely to choose marriage without considering the odds of success and it is challenging to talk reality with people who have stars in their eyes. That said, it would be important for each person to consider what is known about the other person. What does the person say? How does the person act? Are the two reasonably congruent? If not, what is going on? How does this person show love? How selfish is this person? Are there financial issues going into the marriage because one person has not managed money well? Have there been failed relationships in the past for either person? What has been the cause of failure? Does one person have the goal of changing the other person? 
Divorce is potentially devastating for children because of the way in which children think. A child thinks he or she is to blame because the parents are divorcing and that one or the other parent doesn't love him/her well enough to stay. Children especially suffer when there is a protracted, cantankerous custody battle and they are pushed to choose sides. 
The only time divorce is somewhat less devastating is if the children have witnessed domestic violence between partners and that carries its own emotional baggage for children. 
Divorce profoundly affects all who are involved and it would behoove the potentially-married to consider all these things and work to change them before the vows are said.