Exploration is considered essential to infant learning, but few studies have quantified infants' task exploration. The purpose of this study was to quantify how infants explored task space with their feet while learning to activate a kick-activated mobile. Data were analyzed from fifteen 4-month-old infants who participated in a 10-min mobile task on 2-3 consecutive days. Infants learned that their vertical leg movements above a systematically increased threshold height activated the mobile. Five kinematic variables were analyzed: (a) exploration space volume, (b) exploration path length, (c) duration of time in the region of interest around the threshold that activated the mobile, (d) task-specific vertical variance of kicks, and (e) non-task-specific horizontal variance of kicks. The infants increased their general spatial exploration, volume, and path, and the infants adapted their exploration by maintaining their feet within the region of interest, although the task-specific region increased in height as the threshold increased. The infants used task-specific strategies quantified by the increased variance of kicks in the vertical direction and no change in the horizontal variance of kicks. Quantifying infants' task exploration may provide critical insights into how learning emerges in infancy and enable researchers to more systematically describe, interpret, and support learning.