You don't "have to" weigh any particular weight. However medical
people have created tables to show what are average weights for
different people and what weights are considered healthy.
It depends on your height. If you are average height for 10
years old, it ranges between 70-85 pounds. Personnaly, I am only 61
pounds. I am average height and I'm underweight. I never finish my
plate and I say I'm full.