This book, by Wendy L. Moss, Ph.D, offers some ways for children to calm themslves when they are experiencing challenging emotions.
Mind Yeti for English-speaking families: Mind Yeti
Mind Yeti for Spanish-speaking families: Mind Yeti Espanol
Applying the GLAD Technique is very simple. All we need is a journal (a notebook works too) in which you can record one thing:
G: One Gratitude that you have.
L: One thing you learned today.
A: One accomplishment you did today.
D: One thing that delighted you today.