There have been a number of kids music songs about Pluto -- I'm most partial to Rocknoceros' "Pluto", but the Nields' "Percy on Pluto" and They Might Be Giants' "How Many Planets?" (off their forthcoming Here Comes Science) are pretty good, too.
The Music Tapes, which is the brainchild of Julian Koster, who also played in Neutral Milk Hotel, doesn't have a kids music album to its credit. But this song, "For The Planet Pluto," features some kids, plus a singing song. As a standalone kids' song, it's only so-so, even with the singing saw. But as a video, nothing else I've seen (or heard) more eloquently demonstrates why people -- especially kids -- reacted so strongly to Pluto's dismissal from planetary status. (It's even better than TMBG's video, which is pretty darn good.)
If you like this, there's more on its way... stay tuned...
The Music Tapes - "For the Planet Pluto"