I agree with Gustavo's interpretation, although I find the original passage poorly written. I would prefer "gets somewhere between" instead of "gets anything between". Your misspelling of "youngsters" is a slight distraction, but not nearly so much as what the authors seem to want to mean by the word. (Also not nearly as much as the huge difference in meaning between their "between two and five hours' sleep a night" and your "between two and five hours' sleep at night".) They appear to equate the words "teenager" and "youngster". By the time I was seventeen I was self-supporting and had little communication with my parents. I was attending Kent State University and typically got ten hours of sleep a week. Is this what we call a "youngster"? When I was living at my parents' house, I was required to go to bed at nine o'clock PM (that was in high school; before that it was eight o'clock). Lights out. If I was caught reading a book, I was punished. I would stare at the ceiling in the dark, hour after hour, night after night, and finally start to drift off to sleep around seven o'clock AM, just in time for my alarm clock to go off. The only actual sleep I ever got during my grade school years was in my classes.
I really can't begin to describe how poorly written your source information is. They say that "medical experts" say that one in five "youngsters" get two to five fewer hours of sleep per night than their parents did at their age. Or, at least, that's what they would have said if they had the literacy that I would expect of a twelve-year-old. How much sleep do the rest of them get? Seven hours less? Ten hours more? What is the median, or the mean? How many medical experts are we talking about, and what is the sample size of the youngsters? These statistics are absolutely meaningless as presented. In fact, they're much worse than meaningless. They are dangerous. They are deliberately vague in such a way that they can be manipulated to support any subversive purpose imaginable.
When I was younger, there was a lot of advertising that spoke of the opinions of "four out of five doctors surveyed". So what? 999 out a thousand people in authority during Galileo's lifetime would have had him silenced permanently for suggesting that it was possible for the Earth to move. In contrast, "four out of five doctors" seems to be a rather insignificant majority. In particular, I remember a series of television commercials saying that "four out of five dentists recommend sugarless gum for their patients that chew gum". In the first place, I find chewing gum disgusting and would like to see it outlawed. In the second place, one of the most popular brands of sugarless gum at the time was Trident, which is derived from a Latin phrase meaning "three teeth". I am not making this up.
But again, we have some unknown number of "medical experts" spouting their dubious opinions, and I'm not seeing any source information to identify these experts, nor their credentials, what they actually said, how they gathered their statistics, etc. At least in the days of "four out of five doctors surveyed", we could at least imagine a Doctor I, a Doctor II, a Doctor III, and a Doctor IV. But then we have this rather significant 20% that disagrees. Even as a child, I always wondered, what does the fifth doctor think, and why? Wouldn't medicine, and, in fact, all other fields of technology, science, linguistics, and anything else that depends on progressive thought have stagnated centuries ago if it weren't for maverick thinkers of every generation daring to challenge the majority views of their day?
But, of course, that's just one man's opinion. I could be wrong.