First, it's a confirmation of your child;s achievement. The minimum rating requirement is not easy to satisfy. Your child;s hard work didn't just get wasted.
Second, it's a great opportunity to represent your country, USA, similar to the sportsmen in Olympia. (In fact, there is a chess Olympiad every two years). This is an honor.
Third, it's a chance to visit other countries, learn other cultures, meet kids from other places in the world, and make life-long friends from anywhere who also love to play chess.
Fourth, the intensity of the competition, the positive feedback of the qualification, and the rich experience will motivate your child to work even harder when s/he comes back. The momentum will carry him/her forward. We often see their rating go up a lot in next few months.