What is the average weight of an 8-year-old?

For an 8-year-old girl or boy there is no particular or perfect weight. Weight is related to height and body composition rather than age. For in-depth information about weight in relation to height (or how to deal with unhealthy weight gain in children) and to see charts showing the distribution of weights and heights of children at various stages, please see the page link, further down this page, listed under Related Questions.
i would say any where in between 50-70 pounds. it all just depends on the size of your child (in height)