Gratitude can, of course, be demonstrated through a simple spoken, "thank you" when someone else does something special for you. But perhaps a dying form of gratitude is the "thank you" note. My preschoolers learned that it's best to always send a "thank you" note to anyone who did something special for us--the firefighters who came to visit us, the parent who brought in cupcakes for a birthday, the administrator who got us new writing supplies. The notes started out as a whole-group activity. We would sit together crafting the words to use and everyone would then sign the end-product. Towards the end of the school year, though, something completely amazing would happen. The children began writing thank you notes on their own. They would thank each other for little things--opening the door for recess, sharing toys, being good friends. They would write thank you notes to their parents and siblings. It was a wonderful transformation to see for four- and five-year-olds. Of course, the best way to teach gratitude, along with other character virtues, is to model what you want to see from children in everyday situations. Consistency is key!
Here are a few other resources on teaching gratitude:
Prep them to be grateful,
The Prepped Parent