In recent years, the reduced ability of infants to control their body movements has been studied. However, no appropriate exercise program based on the evaluation of physical control itself has yet been developed and implemented. Therefore, we have suggested that measurement and evaluation of the motor performance of infants should focus not only on their performance but also factors during the movement process itself. The aim of the present study was to acquire knowledge about an effective exercise program to promote the development of body control ability. For this purpose we used a task involving hopping on an elastic surface (the HES task) that requires higher body control ability, and examined the factors and movement characteristics related to task accomplishment. First, we evaluated the relationship between the HES task and other elements of physical strength (foot balance, standing broad jump, and side jump). Second, we studied the head position, tilt of the legs, direction of the toes, and line of vision at the time of landing during the HES task by using an easy method of observation evaluation, and assessed the influence of these factors on the task. The results of this study are summarized as follows: (1) The HES task was significantly correlated with the standing broad jump and side jump. (2) The time required to complete the HES task depended on a quick landing. In addition, head stability, tilt of the legs, and movement of the eyes before landing were found to be important factors influencing a quick landing. These results suggest that body control during rhythmical hopping on an elastic (unstable) surface can be assessed by studying the head position, line of vision, and tilt of the legs during the HES task.