The development of 3 to 6-year-old children's orienting activity was investigated by examining the accuracy of their estimation as to whether they could jump over an object. Sixty children in each age group were put into three different conditions of jumping. In Standard Condition, the children stood in front of a white line and stepped back as far as possible from where they judged to be able to jump and then were to jump from there. In Physically Loaded Condition, the children performing under the same condition as described above except for a cushion they were to hold in their arms. In Objectively Loaded Condition, the similar procedure was employed except that the children had to jump on a 30×30cm-mat whithout falling out of it.Analyses of the discrepancy between their estimation and actual performance showed that (a) orienting activity developed all through the 3 to 6 year-old bracket, and (b) 6-year-old children's orienting activity was shown differenciating according to conditions.