If a 9-year-old weighs 50 pounds is this weight good?

It is difficult to know without more detail from you. Weight is related to height and body composition rather than age. Please feel free to ask the question again and include more detail. Alternatively, for more information about weight in relation to height, and to see the distribution of weights and heights of children at various stages, see the page link, further down this page, listed under Related Questions.