This is an incredible film worthy of Truffaut's debut as a director, and a wonderful introduction to the French New Wave. Never having seen a piece the belongs to the New Wave, I think this short really speaks volumes for the direction style apparent in later works by Godard, Truffaut, Melville, etc... The use of the hand-camera and on-location filming really creates a completely different experience than the Hollywood studios of the same era.
The natural lighting in the forest scenes in this film is, by itself, beautiful. The hand-cam following via a reverse shot is a great introduction to the movie. The shadows of the trees on the ground contrast very strongly with the lighter elements of the location. One can understand the feeling the boys have for Bernadette almost solely through the mood set by the imagery and music in the scene; naivety, lust, and love.
As Gerard is introduced, very subtley, a negative portrait is painted for the character. Most obviously, the narrator is one of les mistons, so he does not say positive things about Gerard. Aside from narration, the location changes from the forest to the city, and lighting is a bit darker. The energetic joyful music is also replaced by background urban noise. The mood of the movie has completely changed, and the audience is inclined to sympathize with the kids, and not Gerard.
One of the best qualities of this short is what is chosen to be shown. The boys are shown playing soldiers, and tricking an old man, for example. Gerard and Bernadette play tennis, but even small scenes of movement through the city or country are shown. In a short film, it would seem strange to show such mundane activities and include so little dialogue, yet these are the things that are actually important to the film. It seems in Les Mistons, that actions take precedence over words, most likely because they are more visually interesting.