The general rule is that both parents are entitled to the have custody of their children in the absence of a court order otherwise. If a dad has been served with notice of divorce, he might be able to take custody of the children immediately. The dad may also be able to take custody at a later stage of the divorce proceedings.
Divorce proceedings are conducted under state law and different states have different procedures. All states, however, determine child custody using the best interests of the child standard. The factors used to determine that standard can vary between states. Generally, courts look at any relevant evidence to determine which parent should have custody of the children and when. All states have laws that prevent a parent from taking custody of the children in violation of a court order. These laws can include civil punishment or criminal charges.
All states have a procedure by which one parent in a divorce can ask the court for a court order of custody, called an "ex parte" order. If you request the order, you must file an affidavit with the court stating the facts necessary for the order. In some states, there must be an emergency for the court to issue an ex parte custody order. Other states routinely allow ex parte orders at the time a divorce is filed so there will not be conflicts as to which parent has custody of the children before the court can hold a full hearing. Generally, following an ex parte order, the court must hold a hearing withing a specified number of days, if requested by the other parent. If the dad is served ex parte custody orders along with the divorce papers, he may take custody of the kids only at the times specified in the order. For example, if the order states the dad has the children every other weekend, that is the only time he is entitled to take custody of them.
Courts can hold custody hearings to make temporary orders that will last until the divorce is final. Different courts conduct these hearings in different ways. They are, in effect, mini-trials. You and your spouse submit evidence to the court and ask the court to make a decision. In some cases, courts hear from witnesses and follow the full rules of evidence. In other cases, courts will shorten the hearing by asking that some evidence be briefly presented to the court by the parties and their attorneys. A judge can grant a dad custody in a temporary order.
When the divorce is final, the court will enter orders of custody. These can include giving full or joint custody to the dad. You and your spouse can agree on how you want the custody of your children to be determined and ask the court to accept that agreement. If you cannot agree, states have different procedures that you and your spouse must follow. Courts often order you to mediation, an evaluation by an expert and parenting classes about the effects of divorce on children. As a last resort, the court will hold a full trial and determine custody of the children.