The prototype of "Happy Birthday to You" is a song called "Good Morning to Everyone" written by Mildred J Hill &; Patty smith), the lyrics are catchy: "Good morning/Good morning/Dear children/Good morning". At that time, the Hill sisters were kindergarten teachers, and Good Morning to All was originally a song sung when teachers and students exchanged greetings in the morning.
Happy birthday to you, often called Happy Birthday or Birthday Song, is a popular song to celebrate your birthday.
According to Guinness World Records, "Happy Birthday to you" is one of the three most popular English songs, and the other two are "Forever Friendship" and "Because he is a happy and good man". This song has been translated into many languages, although in some countries where English is not the main language, people often sing English lyrics of this song.
References:
Happy birthday to you-Baidu Encyclopedia