Can preschoolers be depressed?

Looking at the story, Can preschoolers be depressed? I can't think of a better situation to place this to an excess nation. The questions raised in the story,
"Is it really possible to diagnose such a grown-up affliction in such a young child? And is diagnosing clinical depression in a preschooler a good idea, or are children that young too immature, too changeable, too temperamental to be laden with such a momentous label? Preschool depression may be a legitimate ailment, one that could gain traction with parents in the way that attention deficit hyperactivity disorder (A.D.H.D.) and oppositional defiant disorder (O.D.D.) — afflictions few people heard of 30 years ago — have entered the what-to-worry-about lexicon. But when the rate of development among children varies so widely and burgeoning personalities are still in flux, how can we know at what point a child crosses the line from altogether unremarkable to somewhat different to clinically disordered? Just how early can depression begin"
strike at the whole issue of what is 'normal' or a 'standard' and appears to be a slippery slope to 'explain' the behavior of human beings. This raises a question in my mind, is it necessary to account for everything about humans? In this particular story, and in psychiatry in general, we have a whole terminology about egos, alteregos etc. which form the basis for the whole field, and this leads another question of language itself! We have based a whole profession on a language, which then becomes a basis for all the measurement afterwords.

I understand that the thoughts are very rudimentarty and might not be related to the original purpose of excess nation, but I am starting to wonder if my terminology and understanding are adequate or not.

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