Prenuptial agreements are useful for many things, but figuring out custody arrangements before you have children or before the possibility of a divorce is not something they are meant to address. If you think about it, planning that far in advance would be detrimental to both the children and their parents. The situation the parents face now may be completely different at the time of a divorce. Children grow and change as well, requiring special care and having different needs.
Although prenuptial agreements won't help with child custody or parenting arrangements before a divorce, they do help with past children. For example, if you want to provide for children you bore during in a previous marriage or relationship, you could use a prenuptial agreement that addresses your estate plan and protects your heirs.
Why don't prenuptial agreements address custody?
It's too complicated to predict what a situation is going to be like before divorce, and therefore, addressing custody arrangements in advance would not be in the best interests of the child. Prenuptial agreements may not include any details on child support or child custody issues because the court holds the final say in these matters.
Here's an example of a prenuptial agreement with terms that won't hold up in court. If two people have an arrangement where the child will only be cared for by the father once a month for a weekend and the mother dictates the full cost of child support, the court will not allow it. The court will make sure both parents are fit to parent before deciding on custody matters. Additionally, the court has the final say when it comes to child support since this is often based off of state guidelines.
What else can't be in a prenuptial agreement?
It's also not allowed to include provisions where one person gives up the right to alimony or where divorce is encouraged. For instance, encouraging divorce to obtain compensation or requiring divorce upon pregnancy would never be a term allowed in court. Likewise, no person can deny the other a right to attempt to gain spousal support in most cases. Every state approaches this differently, but in most cases, the provision will be struck down because it is seen as unfair to a spouse who does not know what his or her life may be like at the time of a divorce.
Overall, nothing to do with child custody or support are acceptable in these documents.