Though it isn't a good movie for children six and under due to fighting and killing, the movie has a lot to teach older children about respect, fairness, compassion, goodness and evil.
The movie was darker than I expected, but it was good in spite of that. These Hogwart's kids are growing up and growing into their "powers". They are taking on responsibilities that, in a way, parallel real life, and are going through that teenage angst just as a real teenager would. Combine that with the good -v- evil theme, and it becomes a soup that works well.