The purpose of this paper is to clarify the relationship between children's cognitive space, as well as activities and their development. The children of the Kasugai Primary School in Aichi Prefecture were studied by means of questionnaires and interviews.The investigation revealed the following facts:1. The sphere of activity of children in the third and fourth grade is within seven to eight kilometers if they take a tram and they like to explore unknown places. This sphere of activity is larger compared with the 300 meters sphere of activity of kindergarten children and the first or second grade pupils whose sphere of activity is only one kilometer.2. In this case, the Nagoya Airport to the west of the school has prevented children's activities. However, the existence of bicycle paths and railroad (Komaki Line) has brought about children's activities.3. Nevertheless, fifth or sixth grade pupils still make use of the many playing fields near their homes, for example, the beautiful parks, vacant lots, haunted houses and secret hideouts.In conclusion, this study shows that the daily activies of children help in the development of their cognitive space.