I see you have received lots of suggestions for songs...

Here's a thought...take the music for 12 Days of Christmas, or any of the other cumulative melodies, and change the words to suit your needs. You can do this with any other simple melody you know too. My Latin teacher used to use the Mexican Hat Dance melody to teach us verb congigations in High School. I still remember them. I use this technique with my pre-K (with disabilities) students as they learn English and it works really well because I use familiar melodies and then re-use them so they remain familiar and they can worry about learning the words, not the song. You may even want to use a Japanese folk melody that they already know and could teach you.
Kudos to you for using music to teach language!

Also, there is a wonderful book called Alaska's 12 Days of Summer by Pat Chamberlin-Calamar and Shannon Cartwright (Mar 2003) that goes to the tune of 12 Days of Christmas but adds a new animal each verse. Things like grizzly bears, moose, wolves, and other common Alaskan animals which is simple but not jouvenile and could be useful. I find having pictures to help represent the words students are learning moves things along 10 times faster.

Good Luck!