Mo. Rev. Stat. § 452.425

Any court order for the custody of, or visitation with, a child may include a provision that the sheriff or other law enforcement officer shall enforce the rights of any person to custody or visitation unless the court issues a subsequent order pursuant to chapter * 210, 211, 452 or 455 to limit or deny the custody of, or visitations with, the child. Such sheriff or law enforcement officer shall not remove a child from a person who has actual physical custody of the child unless such sheriff or officer is shown a court order or judgment which clearly and convincingly verifies that such person is not entitled to the actual physical custody of the child, and there are not other exigent circumstances that would give the sheriff or officer reasonable suspicion to believe that the child would be harmed or that the court order presented to the sheriff or officer may not be valid.