All of the situations you describe, you are right. There does come a time when, perhaps, school-age children (not preschoolers, including five year olds) can handle out-of line-of-sight supervision, depending on the environment in which said freedom is granted. In some areas, going to the park or riding bikes is okay for school age children, as long as they know the dangers. Other environments it might not be safe. Exposing a preschool child to any physical dangers, such as water, stairs, flying balls, firetower steps, busy streets, etc etc. a child would not recognize or maybe even notice the dangers and adults need to be responsible for them.