The purpose was to compare the effect of low- and high-gain visual feedback on ankle movement variability and muscle activation in children and young adults. Six young adults (19.8 ± 0.6 years) and nine children (9.4 ± 1.6 years) traced a sinusoidal target by performing ankle plantar/dorsiflexion movements. The targeted range of motion was 10°, and the frequency of the sinusoidal target was 0.4 Hz for 35 s. Low-gain visual feedback was 0.66°, and high-gain visual feedback was 4.68°. Surface EMG was recorded from the tibialis anterior (TA) muscle. Movement variability amplitude was quantified as the standard deviation of the position fluctuations after the task frequency was removed with a notch filter (second-order; 0.3-0.5 Hz). We quantified the oscillations in movement variability and TA EMG burst using the following frequency bands: 0-0.3, 0.3-0.6, 0.6-0.9, 0.9-1.2, and 1.2-1.5 Hz. Children exhibited greater movement variability than young adults, which was exacerbated during the high-gain visual feedback condition (P < 0.05). The greater ankle movement variability in children at the high-gain visual feedback condition was predicted by greater power within the 0-0.3 Hz of their movement variability (R (2) = 0.51, P < 0.001). The greater power in movement variability from 0 to 0.3 Hz in children was predicted by greater power within the 0-0.3 Hz in their TA EMG burst activity (R (2) = 0.6, P < 0.001). The observed deficiency in movement control with amplified visual feedback in children may be related to an ineffective use of visual feedback and the immaturity of the cortico-motor systems.