I took my 8 year old daughter to this because, well, I wanted to see it. There are some moments that are a little intense and distressing as the protagonist is discriminated against and manhandled by one evil character in a brief scene.
However, I found that my 8 year old was engaged, completely understood what was going on (minus a couple of questions about how everyone was related, mostly), and was involved to the point of applauding with the rest of the art-house audience when appropriate (I don't want to spoil it for you!).
For Austen fans, you get the look but not the feel - no humor or satire here. Pure drama. Some very chaste romance.
Lots of room for good discussion afterwards about race, gender and income inequality, slavery, social norms, and the awesomeness of period costume.
Equally appropriate for boys and girls. Generally engaging movie and nice to see a black protagonist in one of these. The fact that the story is more or less true makes it that much more interesting.