There are no medical or scientific tests that can prove mental disorders are medical conditions. Psychiatric diagnosis is based solely on opinion.
Yes people experience depression, anxiety and sadness, children do act out and/or misbehave, and yes, some people can become irrational and/or psychotic.
This doesn’t make them ‘diseased’ and there is no evidence of physical/medical abnormality for any psychiatric disorder whether its Attention Deficit Disorder (ADHD), Bi-Polar Disorder, Depression, Oppositional Defiant Disorder, Obsessive Compulsive Disorder or Schizophrenia.
This doesn’t mean that there aren’t solutions for people experiencing difficulty, there are non harmful, medical alternatives.
https://www.cchrint.org/psychiatric-disorders/