Video animation for any grade, but especially PK-4 (shows sacrificing self for others):
http://www.youtube.com/watch?v=p0lynZYyshg
Video for any grade, but especially 4-8 (shows someone doing kind act, boomerangs back to him by end of video):
http://www.youtube.com/watch?v=nwAYpLVyeFU
Video for upper grades, 6-8 (about not judging others by looks and remaining faithful in friendship-Britain's Got Talent):
http://www.youtube..com/watch?v=ZsNlcr4frs4
For the science behind kindness:
http://greatergood.berkeley.edu/article/item/the_compassionate_instinct
For teaching ideas, videos, lessons:
For older students to view and get ideas/inspiration for kindness:
o http://www.366randomacts.org/
o http://www.wikihow.com/Practice-Random-Acts-of-Kindness