YOGA
Cosmic Kids Yoga - Fun, easy to follow Youtube videos with lots of special effects to entertain any child. This is definitely a fun introduction to some great stretching activities.
Fitness Blender Yoga - This is meant for older students. Once you go to the site, search "yoga" and you will find all of their yoga videos. They even have a beginner one that is great for first timers.
Yoga For Kids - Another good option to practice some mindfullness, breathing and stretching.