The typical 3-year-old girl probably believes that she can run as fast as her 6-year-old sister can.

At the age of 3, children are just starting to develop their sense of self and their abilities. They may not yet fully understand that older children are generally faster, stronger or more capable than they are. Therefore, a typical 3-year-old girl may believe that she can run as fast as her 6-year-old sister can.