Pendente Lite Orders
If you separate before your divorce is final, and if you have kids and they stay in the marital home, you or your spouse can petition the court for a pendente lite order setting custody and visitation terms. This usually results in a court hearing, but it's not a full-blown trial. You normally cannot testify, nor can you call custody experts as witnesses. The judge usually reviews your written submissions explaining why you think temporary custody should be awarded a certain way, and he may have a few questions for you or your attorney. It's generally accepted that his ruling is subject to modification in your final decree, after you and your spouse negotiate a permanent parenting plan or you go to trial. If you don't like his temporary ruling, you may not have much recourse. You usually cannot appeal a temporary order, and in some states, you can't even file a motion to modify it. Because the order is considered temporary to begin with, the court will usually wait to revisit custody terms at your divorce trial if you and your spouse can't reach a settlement.
Courts favor stability and continuity in children's lives when their parents are divorcing. At trial, judges will base permanent custody on a series of factors designed to determine what is in the best interests of the children. These statutory factors often include reference to where the children have been living all along, and with whom. For example, Michigan's best interests statutes cite "the length of time the child has lived in a stable, satisfactory environment" and "the permanence…of the existing or proposed custodial home," and these factors can apply to temporary custody decisions as well. If your spouse stays in the family home when you break up, if you then rent an apartment for yourself, and if she petitions the court for temporary custody during your divorce proceedings, the judge is likely going to place the kids with her -- albeit temporarily -- rather than make them move.
Temporary to Permanent Custody
Assuming your spouse gets temporary custody of your children until the divorce is final, you may face the same best interests hurdle at trial when permanent custody is decided -- and now it's become even more formidable. The judge may still be reluctant to make your children move, at least if all other things are equal and you haven't proved that your spouse is an unfit parent. Temporary custody orders often turn into permanent custody orders for this reason. Temporary orders establish a norm for your children during the pendency of your proceedings, on top of the norm created for them while your marriage was intact. If nothing else, the judge has already decided once, early in the proceedings, that your spouse is the more appropriate parent, so you're faced with trying to convince him at trial that his first decision was wrong.
What You Can Do
If custody is likely to be contested in your divorce, speak with a lawyer. Initial hearings for temporary custody are often pivotal to the proceedings and they can help determine the terms of your final decree. At the very least, don't move out of the family home until you've conferred with an attorney.