This Laurie Berkner duet with Tom Chapin is indeed a happy song, but I wouldn’t call it the happiest song I know.
For starters, I would submit that Pharrell Williams’ ‘Happy’ is a happier song than this. R.E.M.’s ‘Shiny Happy People’ is, too. And those are just songs with “happy” in the title.
Way back in ’09, I did a week of happy songs that included the R.E.M. tune as well as Simon & Garfunkel’s ’59th Street Bridge Song (Feelin’ Groovy)’ among others.