I interpret it to be about growing up and how you look at things differently in the process. She sings "I once fell in love with you, just because the sky turned from gray into blue", to show that she fell in love with someone before really knowing what kind of person they were, and the way that line is sung would make it seem like she either misses the innocence and naivety that she used to possess, or that she realizes how foolish it was. The line "I believe in Saint Nicholas, it's a different type of Santa Claus" says that she now knows the difference between fairy tales and reality, seeing as Saint Nicholas was a real person and Santa Claus is a (highly) fictionalized version of him. There seems to be a sound of mourning in the Casady sisters' voices when they sing this song, so I think it's about longing to be a kid again and to believe in fairy tales.
I interpret it to be about growing up and how you look at things differently in the process. She sings "I once fell in love with you, just because the sky turned from gray into blue", to show that she fell in love with someone before really knowing what kind of person they were, and the way that line is sung would make it seem like she either misses the innocence and naivety that she used to possess, or that she realizes how foolish it was. The line "I believe in Saint Nicholas, it's a different type of Santa Claus" says that she now knows the difference between fairy tales and reality, seeing as Saint Nicholas was a real person and Santa Claus is a (highly) fictionalized version of him. There seems to be a sound of mourning in the Casady sisters' voices when they sing this song, so I think it's about longing to be a kid again and to believe in fairy tales.