We found a wonderful book by a fellow Montessorian, Shakta Kaur Khalsa, called "Fly Like a Butterfly". Her book includes great photos and easy-to-follow text and we have shared an excerpt below from her Children's Yoga site.
Ride your Bumpy Camel
Begin by sitting with your legs crossed. Take hold of your outside ankle. This is your saddle. We are going to ride our camel across the desert. Breathe in deeply as you stretch your body forward, chest and stomach out. Breathe out as you slump back, spine is curved, chest is caved in. Keep moving this way and get faster and faster. Remember it is very hot on the desert and we want to get across it quickly! (20-40 seconds)
Bumpy Camel gives you a flexible spine. Keeps your back muscles relaxed and strong. Helps you digest your food.