A medieval Christmas carol here also known as Unto Us a Boy Is Born (Puer nobis nascitur).
Two translations exist by George Ratcliffe Woodward in 192 and Percy Dearmer in 1928. I like the first four verses of Woodward's version with Dearmer's fifth verse substituted in (although Dearmer's third verse about Herod is also good). Woodward's third verse contains the strange word "childer" which is an old plural of child. We use children today.
It is in the top three or four of Christmas tunes in my opinion.