It's a Christmas song for homeless people. It's intended to make homeless people as happy as homeless people can get, as Opie has alluded to many times in the past. "People in the light", "all the children in the light" = non-homeless people who live in the mainstream world and therefore still have hope and happiness in their lives. Emphasis is placed on hope with the line about children. The 'children in the light' are what he sees as what could have been. The "fa lala lala"'s represent the bum's drunkenness and subsequent general disinterest in what's going on around him. Once in a while (in this case once a year during Christmas) he sort of kind of still remembers to give a shit. Anthony's fascist insistence that all Christmas carols be whitewashed 1950's happy horseshit makes me want to brain him with an oversized guinea nutcracker figurine. Does he just feign ignorance, and pretend not to get the obvious?