When Dennis P. (Stefan Pagels Andersen, 12) magics himself some pubic hair, he drops his pants and shouts it from the rooftops (literally). His bare bottom is shown to the camera.
The season 5, 12th episode "Stefans Geheimnis": When Stefan (Christian Blümel, 14) realizes that he's gay he tries to cut his penis with a razor blade, standing nude in the bathroom (side/rear).