Yoga has so many great benefits from focus, energy, strength, flexibility, to increasing positive emotions I think it is a great thing to teach kids.
The Bari Koral Family Rock Band has a song called, The Sun Dance. This is basically the Sun Salutation which is a flow of specific "warm up" yoga moves that get your body ready for the other poses (at least that is my understanding you may feel free to correct me if I am wrong).
I would also think about checking this song out on youtube because the video was part of what caught my kids attention and helped them see what movements to do. Once they get the movements down they could probably just listen to the song and know what to do.