Here's my short list of feature-length "i must-see's":
We Shall Overcome: A Danish film set in 1969 about a 13-year old who, inspired by the televised speeches of Martin Luther King Jr., takes it upon himself to challenge a headmaster and school system who are failing to uphold the newly established ban on corporal punishment.
Treasure of the White Falcons: Think The Outsiders meets The Goonies in Germany. This coming of age movie seems to have everything - children's gangs, lost treasure, a secret cave...I'm there.
The Horror Bus: A Dutch film (based on a popular book series) about Onnoval, an 11-year old who writes fantasy revenge-themed horror stories as a way of coping with his outsider status at school, until one day a mystical (??) being steals his stories and starts bringing them to life. Our would-be villain thus finds himself pushed into the role of reluctant hero, as he sets out to retrieve the stories before anything bad really happens. I like the idea here and the distinction the film seems to be drawing between fantasy and reality, particularly within the context of violent and darker themes, which are such a normal-yet-demonized part of childhood.
Others to catch include many of the short films (several of which were made by teens and young adults), and two more films exploring unique perspectives into boys' culture, The Boy Inside and Boy Called Twist.