The average weight for a 12-year-old girl is 91.5 pounds, whereas the average weight for a 12-year-old boy is 88 pounds. However, children's bodies vary widely and are largely determined by genetics.
Children grow taller at a relatively consistent pace, adding about 2.5 inches to their height every year. They also typically gain about 4 to 7 pounds per year until puberty starts. However, a deviation from the average weight for a 12-year-old does not automatically signify an abnormality. Children and teenagers have growth spurts at varying times. Throughout childhood and adolescence, it is possible to rapidly lose and gain weight or add inches to height.