The age range that is 40 lbs for a child is between the ages of 3 years old to 5 years old.
Some 3 year olds may weigh less than 40 lbs and may weigh only 35 lbs and some 3 year olds may weigh 40 lbs and a 4 year old and 5 year old can weigh around 40 lbs or even 50 lbs for a 5 year old child.
Different children are built different and some children weigh more at a certain age than others and others may weigh less.
The weight range for a 4 year old is between 30 lbs and 40 lbs.
The average weight for a 3 year old boy is 31.8 lbs and the average weight for a 3 year old girl is 30.7 lbs.
The average weight for a 4 year old boy is 30 lbs to 44 lbs and the average weight for a 4 year old girl is 27 lbs to 39 lbs.
The average weight for a 5 year old boy is 40.8 lbs and 38.2 lbs for a 5 year old girl.
The average weight for a 6 year old boy is 45 lbs to 55 lbs and 40 lbs to 50 lbs for girls.
The average weight for a 7 year old boy is 50 lbs and also 50 lbs for girls although the weight for a 7 year old can also range from 43 lbs to 70 lbs.
The average weight for an 8 year old boy is 46 lbs to 78 lbs for boys and 44 lbs to 80 lbs for girls.
The average weight for a 9 year old boy is 63 lbs and 64 lbs for girls.
The average weight for a 10 year old boy is 60 lbs and 54 lbs for girls.
The average weight for a 11 year old boy is 70 lbs and 60 lbs to 70 lbs for girls.