Disabled-World.com states that the average height of a twelve-year-old male is about 58 to 62 inches and the average height of a twelve-year-old female is 60 to 63 inches. These height amounts are shared for children thirteen years of age.
Disabled-World.com also states that the average weight of a twelve to thirteen year old male is about 85 to 100 pounds, while the average weight of a twelve to thirteen year old female is about 100 to 105 pounds. Also, a newborn child will grow in height by about one 1/4 to 1/2 of an inch per month and grow in weight by about 8 oz. per month. This obviously is not true once children mature into toddlers; since most species tend to grow more rapidly at the beginning of their life, and decrease in growth rate at a virtually exponential rate as they age.