This movie does a lot of things very well. The two main characters, Jess and Leslie, are outsiders at school who deal with bullies. Jess is also a talented artist in a poor family struggling to make ends meet, and his parents and older siblings don't understand him. He and Leslie, though, understand each other and form a powerful friendship.
The movie handles these issues with real sweetness and insight, but then 3/4 of the way through it shifts abruptly into tragedy. (I hadn't read the book or any reviews, so this was a total shock.). At this point, the movie wants to be about dealing with and learning to move on positively from death. That's not a terrible goal, and there are some good scenes after the death, but it's a little trite too.
The death is so so sad - my 8 yr old daughter has never cried as much from a movie as she did here, and I was bawling too! But I do think she understood the message and that overall it was a positive experience for her. I wouldn't let kids younger than that watch it and would consider the emotional maturity of kids from 8-11 and whether you even want to confront tragedy with kids that age if you don't have to.