Both my wife and myself have always been involved in volunteering for various things, meals on wheels, food pantry, etc. So Amber has been exposed to the idea of contributing to those less fortunate since day one. Plus, she's exhibited a nurturing nature most of her life, it's only lately that it's begun to focus on various things. My wife, who is the CFO of the house, also regularly donates money to several charities that have earned our trust. Involving Amber with the process, both as financial instruction and example.
Somebody at the local library made an excellent suggestion yesterday, when I brought Amber's used books there. Holding a special yard sale for kids to sell their unwanted items in the local park. It would be a kids only affair, with adults just supervising or providing snacks and drinks and just making it a fun and educational experience for the kids.
Obviously not something for younger kids or ones that can't grasp the concept of getting rid of stuff. But, it wouldn't hurt to expose them to something like that on a smaller scale. It would depend upon the individual kid.