Check out Kids Yoga Stories on this link for a free poster to use in your classroom for mindful movement:
https://www.kidsyogastories.com/yoga-in-the-classroom/

This is a great article on edutopia that gives some simple but effective steps to build a school-wide mindfulness program. I think the most important are steps 4 and 6... to teach children about mindfulness, educators must understand what they are teaching and why!

https://www.edutopia.org/blog/implementing-school-wide-mindfulness-program-patrick-cook-deegan​