Many children are very satisfied with doing proper work. The Building Sites give them the opportunity to realistically mimic the working world of adults. Heavy loads can be moved over a roller, sand and water can be poured into pipes or gutters, a sand wheel can be turned, the dumper box takes a load of sand and a bucket is filled. Co-operation results from carrying out a mutual purpose, while physical laws are unconsciously recognised and brought into play. The structure should stand in a sand or gravel surface for ensuring the best play value.