I recommend setting the mats in two lines (so students face each other Ashtanga-style) for the beginning of class, and then slide them out into a circle so everyone can see as you turn the pages and read from the book between poses.
Music: If you want to incorporate music into the lesson (for sun salutations, the movement game, the dance party suggested toward the end of the story, or relaxation, Songs for Teaching has a page devoted to music about this theme.
Mirror Game. Start seated in easy pose (legs crossed) facing your partner. Tell one line of mats that they will be the leaders first, and the other side will reflect. Leaders can make faces, move their heads, shoulders, and arms (but remain seated) as the child across from them follows along with their own body. Then let the other side lead.
Still facing a partner, move through some easy sun salutations (Mountain, Gorilla, Plank, Cobra, Dog) and maybe a few other poses if you have time.
Before going on to the next part of class, check in with the students and ask a few questions like, "Does the person across from you actually look just like your reflection in a mirror?" "Does your partner move exactly the way you move?" "Does everyone look the same doing sun salutations?" You will probably get a mixed bag of answers, but make the point that since our bodies are all different, we all move a little differently, and Carter's dog shape is different than Annabelle's dog shape--but that's what makes each of us special!
Movement Game (Need: Music, a bell or other noisemaker):
Monster Match. We will be reading a book about some interesting and cute monsters today (good to add these descriptors so students aren't frightened off by the word "monster.") Let's pretend that we're silly monsters, too! Turn on some music and tell the monsters to move around the room--freestyle or with suggestions like rolling, squirming, swimming, flying, etc--and when you ring the bell, monsters must pair up and sit back to back. Repeat a few times, and when they get the hang of finding a partner quickly, have them match up other body parts when the bell rings--elbows to elbows, knees to knee (Chair Pose), feet to feet.
Yoga (Using "Some Monsters are DIfferent" by David Milgrim)
All of the poses are in sets of two because every few pages, the author describes two different kinds of monsters. I read about a pair of contrasting monsters; then we did the poses for those two, and then looked in the book again before the next set.
Afraid: Practice jumping as though you saw a little worm (like the monster in the book), but landing in a one legged pose and holding it (we tried landing in Tree and Airplane)
Brave: Warrior/Peaceful Warrior (flow between the two poses on each side)
Eat Anything: Upward Facing Tabletop Pose. Go around the room as you hold this strengthening shoulder opener and describe what crazy inedible things a monster might eat (I got answers like eyeballs, bumblebees, grass, hair...) Next stand up and sit into Chair Pose, and pretend to gobble it all up excitedly.
Picky Eater: Seated Wide-legged Pose (We'll say Pizza Slice Pose for this activity). Start taking things off the pizza since the picky eater doesn't like mushrooms, peppers, onions... scrape off the cheese and the sauce (making sweeping movements along the floor in front of you). This picky monster might not even want the crust of the pizza--there's nothing left for her to eat now, not even a crumb (roll backwards into rolling like a ball... or crumb)!
Loud: Lion Pose
Quiet: Butterfly (Cobbler's Pose)
Similar Style: Pose like a mannequin, all the students mimic your pose. Which is not as interesting as...
Different Style: Each student strikes a unique pose that they make up.
Dancers: Dancer's Pose (Natarajasana) and or, have a quick dance party with fun music.
Watchers: Eagle Pose (Garudasana) Variation: Stand with one leg crossed over and bend knees as though you're sitting in a chair. Cross one arm over your body as a support. Rest second arm's elbow on supporting forearm, make a fist with top hand and rest your chin on your hand to mimic sitting and watching something.
Playing Outside: Swimming (Salabasana with arm/leg movements)
Playing Inside: Turtle Pose (Kurmasana)
Likes bathtime: Bathtub Pose (Dhanurasana--Bow Pose)
Doesn't like bathtime: Tip Bathtub over by rolling your Bow Pose over onto the floor.
If you have time, circle up and talk about other differences that make us unique, and how being different from our friends is a good thing because we can learn from and appreciate our differences.
Allow time to rest in Savasana or Snugglebug (Child's Pose), listening to quiet music.