Pediatric mangling injuries are approached differently in children younger than 12 years of age due to growth potential. Bony fixation and free tissue transfers can be technically challenging but result in superior sensory and motor outcomes compared to adults. We present a challenging case of pediatric upper extremity reconstruction following motor vehicle trauma with brachial plexus injury, vascular compromise, bony injury, and denervated muscles. Single gracilis functional free muscle transfer was performed to restore elbow flexion. Medical Research Council improved from 0 to 4 and he was able to achieve active range of motion from 30 to 110°.