Jillian and her son Barry being reunited at the end of the film.
Barry saying 'Goodbye!'
At the big meetup, the aliens first make themselves seen, and align their ships to form the Big Dipper. They'd been seen as mysterious and often frightening up till then, when they show a sense of humor.
The entire first contact scene could be seen as the king of Heartwarming moments. Itís practically everything Humanity could hope for from a real world first contact scenario. The Humans and Aliens communicate in a method that they both understand, the Aliens return all the people they abducted over the past century, and then they peacefully part ways with smiles on both sides, content in the knowledge that neither species are alone in the universe.