The Little Swallow was written by Wang Lu and Wang Yunjie, and composed by Wang Yunjie. It's the theme song of 1957 movie Diary of a Nurse.
Part of the lyrics: Little Swallow wears colorful clothes and comes here every spring. I asked the swallow why you came, and the swallow said that spring is the most beautiful here. Swallow tells you that it is more beautiful here this year.