Should a 12-year-old weigh about 85 pounds or is this too thin?

It depends on the child's height, gender, and overall health. On average, a 12-year-old boy weighs between 75 and 115 pounds, while a 12-year-old girl weighs between 75 and 110 pounds. However, some children may be outside of these ranges and still be perfectly healthy. If you are concerned about your child's weight, it is best to talk to a doctor.