My first answer is non-legal. Discussion of a prenuptial agreement raises difficult financial questions. These difficult financial questions inevitably come up between spouses in any marriage. If it is too uncomfortable to discuss these issues prior to a marriage, imagine how much more difficult it will be years into a marriage or, more tragically, at the time of a divorce.
From a legal perspective, prenuptial agreements quickly resolve conflicts that otherwise may drive up large legal bills and create hostility and conflict between divorcing parties. One example is the value of a business, which can easily cost $5,000—$10,000 in expert consultation fees to appraise during the divorce process. Other examples would be issues involving maintenance [alimony] as well as what is or is not considered separate property.
In the absence of a prenuptial agreement, the court will decide the obligations each spouse owes to the other as a consequence of their marriage. Many people prefer to make this decision between themselves.
However, because children have their own individual needs and rights after divorce, there is very little that somebody can put into a prenuptial agreement that will affect issues such as custody or child support.