The same is true for men and women. The narrative we like to repeat is that men and women are the same except for the shapes of their genitals but there are numerous biochemical and metabolic differences that should affect dosages for several classes of medication [1]. The real tragedy is that many drug trials were never done with women so we may not even be sure of what the doses should should be [2]. The same problem exists with children. These are not simple body weight issues.
I feel like the problem is worse with children due to them having a developing brain, where the impacts of medication can have impacts into changing the very person taking them. I am especially concerned with medication for mental illnesses that are prescribed to children, often times off label, but the risk exists for most any medication.
[1] https://www.scientificamerican.com/article/psychotropic-drug...
[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4800017/