Lot of good, thoughtful answers here. I think part of the answer is people are looking back to when they were kids and the path that has led them and others to 'come back' to 3 rail as adults, and assume that the same thing is important for the future of the hobby. Even on the scale side of things, in N and HO, you read a lot of narratives in Model Railroader and other places how the person 'got into" N or HO as a kid, then got into cars and girls and whatnot, then went to school, got married, etc, then came back as they got older. With O three rail many of us did have them as kids (I am in my mid 50's now, so I missed the 'peak' of the PW Lionel experience, but I inherited trains from my brother), then did come back. I think with the introduce kids to it the idea is even if the kid doesn't get into it then, they will have seen it, and the bug will hit later, and I think there is truth to that. I don't share the picture of young kids today, that they are somehow defective because they aren't in to trains, it must be the internet, must be social media and video games, they are 'easy', etc, I think simply that as always has been, there are other distractions. Back in the 1950's, kid hit their teens, and it was often cars that caught them, or sports, or dating , or doing more in the outside world as they got older...and back then, it was television that was turning them into mindless idiots in the 'great wasteland' as the head of the FCC called it in the early 60's.
I think anything we can do to sell the hobby, to kids and their parents, is important, not just because train companies make money out of things like starter sets that allows them to produce other things, but because some kids will enjoy it, and not to mention the parents might get interested, does happen.
One thing, while trains are obviously an expensive toy, as has been written on here many times they always were, back in the golden age there was a reason Lionel produced things like the scout set and had lower end engines, it was because the PW products were pretty expensive relative to salaries at the time. We think of the layouts we have today, but with kids back then they would get new items for their birthday or Christmas or whatnot, a new switch would be a big deal, a new freight car, engines were a big deal (I was lucky, I got into trains in the early 70's, back when people were selling PW stuff for nothing, 50 bucks and you got a ton of stuff, so price wasn't better back then, it is just that the trains were a hot item and kids would get things piecemeal.
Keep in mind, too, that the hobby has changed a great deal, it is not really a 'toy' any more, even the semi scale stuff is a lot more intricate than most things in the PW period, and the upper end engines, while in relatively price not that far off from the top end of the PW era, offer scale fidelity and features kids could only dream of back then.
If I was going to retitle the thread, it would be something familiar that we need to bring 'new blood' into the hobby, rather than necessarily 'young people' alone. Introducing young people is about planting a seed for the future, the other part is getting new people into the hobby of various ages, so there is a base in the future. I have to agree that with trains across the board it tends to be an older hobby and remembering back when I started reading train magazines in the mid 70's, it always was a hobby of those in their 30's on up, with more than a few gray hairs in it, too.
In some ways there is a parallel with something else I know more than a bit about, classical music, it has the same concerns with 'aging out' of its audience, but I have read articles from a long time ago that talked about the same thing,so perhaps it always has been something older people tended to be attracted to. Another parallel is people worry because thanks to what has happened in schools, with tight budgets and the like, arts/music teaching has been cut back or slashed, so kids may not be exposed to what kids in earlier generations were, and they worry they won't then pick it up later....much like we worry that kids aren't exposed to trains that much, aren't exposed to the model versions either, and thus will never get interested.