What should an American family do if they lost their child's TM6 card before flying back to the States from Thailand?

An American family of 6 is looking for advice on what to do about a lost TM6 departure card for one of their children before their flight back to the United States in May. They have received mixed advice on whether to file a police report and visit immigration for a replacement card, or if they can simply show up at the airport without one. Several comments suggest that for most instances, they can leave the country without issues at the airport, as many travelers have experienced losing their TM6 cards.