Thanks for the reference @&bs! I'm not on social media (except for Chalkbucket ) so these links are greatly appreciated. The one that @JBS posted reminded me of the one that I do with my babies (5-6 year-olds):
Do a bridge on two (small) blocks—hands on one block, feet on other block. Class crawls under bridge. When students can hold bridge long enough, add more students to the block chain (<--you will not regret investing in this). End state: all students are doing bridges except for one who is crawling under everyone else. It's like line dancing, but with gymnastics flair.