I am a 13 year old boy, with waist 29'', about 74.5-75 cm. This is larger than some people, but not fat.
The average waist size of a six year old girl is between 22.5 to 25 inches. The average waist size of a boy of the same age is between 23 and 25 inches.
The average waist size for an 11 year old is- Girl: 25-30 inches Boy: 26-31 inches
A five-year old girl would have an average waist size of 20-22 inches, depending on her height, diet and ethnicity. [From experience]
about a mile.