I found The Circus Ship by Chris van Dusen by accident a few years ago when browsing through my school's library. What a find! I have used it for language-based activities/group lessons in the past, but until now I hadn't used it for a yoga class. I'm not entirely sure why I waited…its a totally fun book that engages kids on so many levels. Language-wise, van Dusen uses a great rhyming rhythm that makes reading - and listening to - this book super fun. Yoga-wise there are so many great animals to act out in the asanas. And Other-wise - the page where the animals are all camouflaged makes for a fun group activity, trying to find all of the hidden creatures. Even better - its based on a true story, which could allow for some inquiry-based extensions if you're using it in a classroom (especially with older kids).
As with some other lessons, I included a language-based "play" activity that could extend the lesson. While I didn't have time to incorporate the play into this particular class, it is an activity I have done in the past with success. Have fun!