Arlington _ What Presidents Eisenhower and Kennedy wanted a half century ago was in the cacophony of the Brackett Elementary School gymnasium. It was 7:40 a.m., not yet an hour after sunrise and still 35 minutes before the start of school. About 50 first and second graders sprung into action as Kidz Bop youth cover songs blasted out of a boom box. Some youths did situps. Some rapidly tiptoed along an agility ladder. Others crab walked and bear walked. Others did squat jumps. Schiavone stopped the music. The children ran to another station. Music on. The boys and girls did step ups, jumped rope, and ran exuberant laps around all the other stations. Their joyous shouting and stomping competed with the music.