The decline in numbers of young people knowing carols (and hymns)is probably not only down to falling church attendances but also the demise of the daily school assembly at which such things were sung. When my kids were at school (they are now 35 and 29) they did still have an annual carol service just before Christmas, but the sort of songs they learned in school music lessons often were "songs from the shows" or pop songs rather than any of those that came up on University Challenge!