"The 400 Blows." Key. $59.98. Francois Truffaut's semiautobiographical debut feature (made in 1959, when he was 29) was one achievement he never topped: It is by far the best of all his films dealing with children. Truffaut gives us the sad part of his boyhood here: tyrannical teachers, loveless parents, a roguish buddy, petty theft and, finally, reform school and escape. Jean-Pierre Leaud (then 14) for the first time plays surrogate Antoine Doinel, and the whole film crystallizes Truffaut's style: elliptic, nimble, swift, racing from scene to scene--just as Antoine keeps racing ahead until, in an unforgettable final image, his face turns back toward us, by the edge of the sea.