-- Question: Are there any medical conditions that can cause depression in children/adolescents?
Answer: There are a number of medical conditions that can create depressive symptoms. Depression almost by definition is low mood, all of the symptoms that we've talked about in the absence of the medical condition that best explains it.
Having said that, there's a number of medical conditions, especially the chronic medical conditions such as inflammatory valve disease that can be accompanied by depression simply because those conditions are very very stressful, and stress tends to bring out predispositions to depression. It also turns out that some rare endocrine disorders such as thyroid disorders can create depressive symptoms in children and adolescents.
But again, this would be depressive symptoms as a function of the medical condition as opposed to the depression that appears to come out of nowhere and is more based on inherent features that predispose kids to feeling depressed.