Elf - The best way to spread Christmas Cheer is singing loud for all to hear

Buddy is the only human working with elf. He knows he doesn't really belong to the elfs' family, so he decides to find his father. Much to his disappointment, his father doesn't care about his sons. The only thing his father cares is work. While he is working in a toy store, he meets Jovie, a girl that is not excited about Christmas. Despite that, Buddy is still attracted to her, so he asks her out. Buddy and Jovie indeed share similar personalities, so they go on well on the first date.

The town doesn't have a lot of Christmas vibe as before, so the engine of the sleight fails to work properly. To reignite everyone's belief in the existence of Santa Claus, they make the audience join them in singing Christmas carol.

Are children the only people believing there exists Santa Claus?  No, it doesn't need evidence to prove it, I believe it anyways.