Mine are boys but I have a:
2 (almost 3 year old) who weighs 34 pounds (has a little belly on him)
4 year old who weighs 38 pounds (skin and bones but tall)
4 year old who weighs 43 pounds (tall and broad- he could be a football player- he is not chubby, just thick)
7 month old- 17 pounds YEA!!!! He was my failure to thrive baby who only weighed 7 pounds at 5 weeks and we skin and bones, but now he has some chunkiness to him.
I think the author was wrong. Maybe if the 2 year old weighed under 20 pounds it would be a cause for concern. Especially being a girl.