This mindfulness exercise I have used in my classroom with great success with children that were having a tough time calming themselves at certain times of the day.
This exercise not only helps children learn about how their emotions can cloud their thoughts, but it also facilitates the practice of mindfulness while focusing on the swirling glitter in the jar.
Try having the kids focus on one emotion at a time, such as anger, and discuss how the shaken verse settling glitter is like that emotion.
If you leave the jar where they can use it with assistance (if glass) it will be a tool they will reach out for in those moments they are struggling.
Peace Harmony & Love