Pretend you are pulling a tiny alligator from your pocket, and ask the children to do the same. "I keep a little alligator in my pocket. You have one, too. This morning we are going to feed our alligators and see how big they can get."
Make a tiny mouth with your finger & thumb, and say in a little voice, "Chomp, chomp, chomp." Make a bigger mouth with your thumb & fingers, then say, in a bigger voice, "Chomp, chomp, chomp."
Each time your motions will get bigger and your voice will get deeper & louder. Use two hands, then two arms, and finally sit on the floor with your legs outstretched, reach for your toes, and make a HUGE mouth.
After the largest "Chomp," ask the children if their alligators will fit in their pockets. Tell them they will now shrink their alligators (with Magic Spray, PSSSSS! or whatever you prefer), and reverse the motions until you have a tiny little movement and a little voice.
Tell the children, "Give your alligator a kiss & a hug, and then tuck him back in your pocket. Your alligator can't come out again until it's time to feed him!"