A 12-year-old boy should weigh around 88 pounds, and a 12-year-old girl should weigh around 91 pounds, according to Disabled World. These weights are just guidelines, and it is important to remember that each child is different.
During late childhood, children go through many changes. Girls tend to grow faster than boys at this age and children may lose and gain weight very quickly. Children at this age go through many growth spurts and the changes in their body weight can vary dramatically.
If a parent is concerned with a child's weight or growth, it is best to talk with the child's doctor who will keep track of his or her growth and be able to diagnose any problems that may arise.