This really surprised me. I heard once that couples with twins, triplets, quadruplets etc. had a higher rate of divorce than couples with fewer children (which isn't actually true, but then again, I heard it from Kate Gosselin), I thought that if that was true, then couples without children must have a much lower rate of divorce than the average. When I began researching it, I found out how wrong I was.
According to Divorcerate.org, "Sociologists believe that childlessness is also a common cause of divorce. The absence of children leads to loneliness and weariness and even in the United States, at least 66 per cent of all divorced couples are childless."
That might be true, but I think that a big part of it is the fact that since there are no children involved, couples don't feel the need to stay together, as many couples with children do for the sake of the children.
This quote also seems to suggest that these couples want children and can't have them, which causes problems in the marriage. This obviously isn't the case for childfree couples.