An average 3-year-old girl weighs 25.25 to 38 pounds, and an average 3-year-old boy weighs 26.5 to 38.5 pounds, according to What to Expect. All children grow at different rates.
A 3-year-old's growth rate slows down compared to the first year, according to Johns Hopkins Medicine. Most children become slimmer and lose the rounded tummy of a toddler. The average weight gain is about 4 to 6 pounds annually.
If there are concerns regarding an underweight or overweight child, BabyCenter suggests ruling out genetics or deficiencies. A child's body mass index, or BMI, determines whether weight and height are proportional.