Very short and maybe common sense, but because I do absolutely zero research you can trust me 100%.
So...why? I think it's obvious, and by think I mean guess, of course. (no actual thinking was involved in this blog post)
Basically, fantasy clashing with reality. Especially in todays world, children have expectations of life based on delusions from self, media, parents, etc. Then, as they grow older and their lives become less and less localized (home > school [kids from relatively close areas] > high school [kids from a larger area] > Job) they confront a world of people less and less directly involved in nurturing them and more so one where people are generally challenging, competitive, and even hostile or obstructive. Instead of being who they are and who they want to be, they realize they must conform to some degree. Yes, some people make being themselves work, but most others will need to begin ceding parts of themselves to get ahead. I think this is a moment of disillusionment and despair for people to closely bonded to their dreams and expectations from childhood.
I'm certainly no doctor. If I was, I'm more like Dr. Phil rather than Dr. House. I even quack with every step. Therefore, you should trust me when I say children shouldn't be treated too much like children sometimes. I wouldn't have them working the grind right out the womb or anything, but I think taking kids around and showing them different areas of adult life would probably soften the period of transition. It requires spending some extra time with your kid and, yeah, I can see why some people get hives just from the thought, but in a real and symbolic way, who better to escort a child through the stages of life than their own parents?
Of course, I have no children. At least I'm sure I didn't. Don't. I definitely didn't lose my kids. But when I smile children scream and this is why you should give this advice some thought. Don't judge a book by it's cover.