My soon-to-be-3rd-grader has always been interested in how society works: who makes sure that the street lights work, who pays his school director's salary (memorably, his classmates believed "she's really rich because she owns the whole (municipal) school"..., what are taxes, etc. We try to explain things without making it too complicated or too far from the truth, either. We want him to be able to enjoy money and handle it well, but not be too obsessed with it.
Since he's crazy about soccer, we talked about some soccer teams actually being listed on the stock market, and how you can't buy others because they are owned by (for example) rich individuals. Of the three supermarket chains we use, one is privately owned, one is a cooperative (of which we are members), but the third is listed. So he bought some stocks in the listed one for his birthday. We don't follow the price actively, but he knows he's received (a few euros in) dividends from those ones and that the price has gone up, too. Then he wanted to buy a few shares in the cell phone company we use with his own money.
He hoards his pocket money and we pay him a (ridiculously high but mathematically simple) interest on it. There's no sign yet of wanting to invest this money, but the balance of saving and investing is looking pretty damn good so far. He's talked about giving to charity, too, but hasn't yet decided on a goal for that, and I don't want to push him either. We're in a society where charitable giving is less common and smaller scale anyway, since taxes do a lot of the heavy lifting on that front.