The purpose of a child custody letter is to provide evidence to the court or mediator that the parent seeking custody is fit, according to LegalZoom. Fitness generally indicates that the party can act for the best interests of the child.
Child custody letters should cover all factors considered by the court in child custody cases, according to Nolo. Such factors may include the general health of the parent, the emotional relationship between the parent and the child and the basic economic situation of the parent. By indicating that a parent can meet the court requirements on such factors, the custody letter can give the court reason to favor one parent over another. Letters may also be used to establish the living situation to which the child is accustomed, as courts seek to continue the status quo and disrupt the child's routine as little as possible.
Since a child custody letter is used to inform and persuade the court, it is typically written by someone who has a relationship with both the parent and the child, according to LegalZoom.
In some cases, all parties in a child custody case must file child custody letters of recommendation, as explained in the court requirements for the Massachusetts Court System.