Child custody awards are never final. They may always be modified or changed, based upon the best interests of the child. Notice I didn't say "needs" or "wants" of the child; I said "best interests of the child." In the Westchester County Family Court, a mother sought to change the parties' Judgment of Divorce which granted her ex-husband sole custody of her children arguing that the kids now wanted to live with her, though it is not entirely clear whether there was a promise of a new puppy or a new car.
Unfortunately for Mom, this was not a good enough reason to remove the kids from their Dad. After trial, the judge correctly stated "while the desires of the children were to be considered, they were but one factor."
Other factors to warrant a change of custody are: which parent has been more nurturing throughout the child's life; sensitivity to the child's feelings; the desire to keep siblings together; parental "fitness"; violence in the home and alienation of the other parent. Really, it doesn't matter what the parents want and sometimes it doesn't even matter what the children want. What ultimately does matter is where, in the Court's opinion, the children would most likely thrive. Every child custody case must be presented with this critical factor in mind.