One of millions of options of how to sing this wildly popular pop song. It already belongs to no one and represents folk art. Pleasant development that awaits us after the main (and the only) lines are sung, will not allow to die of boredom. There are several musical instruments, about a dozen, actually. However, the main sound is from a very perky guitar.
Reference:Mildred J. Hill - Wikipedia
Happy Birthday to You lyrics - Mildred Hill, Patty Hill