The pressing question is, what did people sing on birthdays before the Happy Birthday song was written? The answer: nothing.
According to scholar Elizabeth Pleck, birthday parties did not become common even among wealthy Americans until the late 1830s; modern birthday cakes emerged after 1850; and peer-culture birthday parties, involving children of the same age as the child whose birthday was being celebrated, emerged between 1870 and 1920, after American urban public schools became age-graded. Thus, the prerequisites for the development of a standard birthday song – the proliferation of birthday celebrations that involved a dramatic moment at which a group of invitees, often children, addressed the honoree — may not have been in place until shortly before “Happy Birthday to You” started to become popular.
From an interesting article about the copyright history of the Happy Birthday song.