Creative Vocalises for Young Male Singers

I work with several young students (below the age of 16) including a couple of boys.  Most of these kids are professional actors already.  This is a challenging age to study singing.  The voice is changing or just about to.  Attention spans vary widely in length.  Musicianship, or lack thereof, can be a big issue.  In addition, there is the age difference between us and the balancing act of respect and friendship that occurs in any private lesson situation.  Most of my young female students have done just fine with either the classic vowel exercises that adult students use or the "fun" vocalises devised for younger singers, like "koo-koo-koo-koo-clock!"  But for boys . . . well, the embarrassment issue raises its ugly head here.  Who wants to sing about "koo-koo-clocks?" when you are doing everything you can to appear cool and masculine at the ripe old age of 10 or 12?  So, today I asked one of my young male students to make up his own vocalise.  Just come up with 5 syllables that make up a sentence.  "All chimpanzees rock" was the result.  You know what?  At least it got him to sing out and use his full voice for the first time.  The resulting flow of energy led to more enthusiasm from him for the rest of the lesson and more creative teaching from me.  ("Magic energy belt" and other space-age props were added to help my young sky warrior).  He improved vastly from his last lesson.  I had fun.  I think he did too.  He stayed cool and masculine.  Win-win.