>In addition to this, obesity is generally an indicator that the child is well fed while being underweight is an indicator of malnutrition.

Interesting perspective. An alternative opinion: "Malnutrition is a state of the body in which due to insufficient supply or incorrect absorption of essential nutrients, the body composition changes and the body's functions are impaired. Malnutrition is associated not only with reduced body mass index but also with obesity." https://pubmed.ncbi.nlm.nih.gov/34749356/#:~:text=Malnutrition%20is%20a%20state%20of,index%20but%20also%20with%20obesity.