This song is about innocence(in this case the Little girl in the dress of snowy white) and protecting it. "If you stray, you'll become a cautionary tale" means that people who have lost their innocence (mainly children) are used as a tale to others to help them keep their innocence.
However everyone gives up their innocence when they grow up, giving it away
This song is about innocence(in this case the Little girl in the dress of snowy white) and protecting it. "If you stray, you'll become a cautionary tale" means that people who have lost their innocence (mainly children) are used as a tale to others to help them keep their innocence. However everyone gives up their innocence when they grow up, giving it away