It's can be a pretty tricky topic to explain to most adults, and touches on the financial crisis, credit default swaps, the decline of the labor movement, Glass-Steagel, Citizens United, etc, so I struggled a bit about how to explain it to a 10 year old. Rather than tell her, I decided to pose a situation and ask her some questions about it.
Me: Imagine if the whole country were just a group of 100 people, and they had 100 dollars of money to between them.
Me: How much money would every person have if they all had the same?
E: that's easy, one dollar.
Me: Right. Now you know that some people have more money than others, so how much money do you think the richest person has?
E: hmmm.... I don't know. 5 dollars?
M: OK, then how much do you think the poorest person has?
E: there are people in the world who don't have anything at all!
M: true, but I'm talking about in this pretend country that we just made up that has 100 people and 100 dollars.
E: right. The poorest person would have 5 cents I think.
M: OK. So how much money do you think that the richest 1 person would have to have before the poorest 50 people would get really mad and start to protest the situation?
E: uuuhhhh.. hmmm... if the richest person had 25 dollars that would be a lot.
M: OK, then how much would the poorest 50 people have combined?
E: I guess 50 dollars?
M: I don't think that would work. Because if the richest 1 has 25 dollars and the poorest 50 have 50 dollars, then that leaves only 25 dollars for the almost richest 49 people. So I think with that example, if the richest 1 had $25, then if everyone else had exactly the same, they'd each have about 75 cents each. Which would mean the the poorest 50 would have about 35 dollars combined. But that's not really likely since some people have more than others.
E: ok, so I guess if the poorest 50 people had 25 dollars combined, then they would be really mad and protest.
M: OK. Do you want to know how it really is now?
M: the richest person has about 40 dollars and the bottom 50 have about 1 dollar between all of them combined.
Her eyes got really big, and she understood why so many people are so pissed off. Then we got in the car to pick her brother up from basketball practice. We took the long way there so we could drive past City Hall and see the protesters. We passed them at about 7:15pm, while they were in the middle of a General Assembly. Hundred of people listening to each other. Quietly, peacefully making the point that enough is enough.