The effect of vocal intensity on vocal efficiency (VE) for children as compared to adults is investigated, leading to the conclusion that children have different VE values than adults. Vocal efficiency was measured using a logarithmic form of the ratio of the acoustical power radiated from the lips to the aerodynamic power supplied to the glottis for voice production. Sixty subjects participated in this study, including 20 subjects with 10 males and 10 females in each of the three age groups: 4-year-olds, 8-year-olds, and adults. The speech tasks were produced at soft, comfortable, and loud levels, and the VE measurements were mathematically adjusted to account for the sound-pressure level variations within each intensity level among the subject groups. The VE values were compared for age, intensity, and gender differences. The results indicate that 4-year-olds and 8-year-olds have lower VE values than adults. Vocal efficiency increased with vocal intensity for all the age groups, and no significant differences were found for females as compared to males. Factors influencing VE such as maturation of the vocal ligament, amplitude of vocal fold vibration, fundamental frequency, tracheal pressure, as well as the source spectra are discussed.