The legal world is an adult world. Children cannot, in most cases, sue. When their parent's divorce in St. Louis, they are part of the custody arrangement, but their input is limited by their age and maturity, and even if a judge takes it into consideration, it is simply one of many factors that will be weighed.
So they have to rely on their parents to protect their "best interest." The judge, too, is supposed to make decisions in the child's best interest. And what is that best interest? In one sense, the best interests of the child are that they should be allowed to grow up being treated as a child.
Their parents should treat them as a child, and not as a pawn or proxy in their disputes with the child's other parent. A parent needs to demonstrate to his or her child their unlimited love, and they can do that by setting aside their own hurt, bitterness and discomforts at the ending of their marriage relationship and focus on their new relationship, embodied in their parenting plan, to do what is right for their child.
This is not easy. Children, as they grow up, may be difficult and have their own challenges. They may attempt to play their parents off each other, and they may be emotional if they feel as if they are being used as pawns by the parents.
Conflict elimination is probably the most important element of your post-divorce relationship. You likely divorced because of stress and tension within the relationship. It does no one, most especially, children, any good to continue that conflict in perpetuity.