We compared 5-year-olds' and adults' sensitivity to moving second-order (SO) gratings in four combinations of temporal frequency (TF) and velocity (V). Contrast was modulated over trials to measure the minimum contrast modulation yielding 82% correct responses. Adults and 5-year-olds (n=64/ age grp) provided individual thresholds for one of the four TFxV conditions (TF = 6Hz and V = 6 or 1.5 d/s; TF = 0.75Hz and V = 6 or 3 d/s) and for two tasks (direction discrimination and discrimination of a moving from a simultaneously presented static grating). Five-year-olds had higher thresholds than adults for all TFxV conditions, especially when TF = 0.75Hz. Control studies with an orientation discrimination task indicate that 5-year-olds' higher thresholds cannot be explained solely by poorer sensitivity to the patterns. When TF = 6Hz, but not when TF = 0.75 Hz, participants at both ages were more sensitive to SO information when the task was to discriminate a moving from a static grating than when it was to discriminate direction. Based on Seiffert and Cavanaugh (1998), it is likely that when TF is 6 Hz, participants use position-tracking mechanisms to discriminate direction and they use flicker-sensitive mechanisms to discriminate a moving from a static grating. At lower TFs, they likely use position-tracking mechanisms for both tasks (Seiffert & Cavanaugh,1998). Thus, the differential immaturities evident in the results likely reflect different rates of development for these underlying mechanisms.