According to the Center for Disease Control and Prevention, the average weight for an eight-year-old boy is 25.75 kilograms, or 56.77 pounds. The average weight for girls is 25.76 kilograms, or 56.79 pounds. The average BMI (body mass index) is 15.78 for boys and 15.83 for girls.
According to the Center for Disease Control and Prevention, average weight and BMI cannot be used to determine if an individual child is at a healthy weight or not. Because children grow so quickly and vary in individual growth, a doctor's opinion is necessary to determine the ideal weight for any eight-year-old.
While children who fall within the average weight for their age are probably at a healthy weight, it is necessary to see a doctor to know for sure.