We have this discussion from time to time, it seems to be up there with why train quality is bad, why trains are so expensive, etc. Kids today do face a different world, and yes they face different times then kids in the past. Some of the reasons kids may not be into trains are the same as they once were, back in the 1950's and 1960's you had television, you had slot cars, you had model rockets, you had organized sports for kids (little league), plastic models, a ton of games and toys that didn't exist pre war or even in the 1950's. Because of cars, kids had access (through a parent driving them) to other activities, not just sports...and if you remember, trains were kind of on life support (talking Lionel here), not to mention kids discovered HO and N scale trains, that were cheaper and allowed them to have much more of a layout in the same space......
Kids back then were also in a different world, back then most kids had stay at home parents, usually the mom, today that is true in only 15% of households...and back then, dear old dad likely worked hard, but likely worked locally and worked pretty much 9-5, these days most people who work have to commute significant distances (they don't work locally), and then also are working longer hours then our dad's generation did, by a long shot, people typically are averaging close to 9 hours a day on work (not to mention what they often bring home), at least in white collar jobs.
Kids themselves also face burdens we didn't, they face pressures we didn't, the rest of the world has influenced what goes on in this country, and kids today with school are overbooked because of the obsession with homework especially, and the idea that everything they do as a kid will make or break them as an adult (not even going to mention what I think of the mania with standardized tests, not the forum for it). I have heard people my age talk about how rigorous their school was, how much they had to do, and quite honestly it is selective amnesia, other than maybe some prep schools, we didn't have a 10th the pressure these kids do, you see little kids with huge backpacks, and kids in grade school have several hours of homework, kids in high school are often doing homework until 1am, it is a different world then we had (put it this way, the local high school today offers something like 13 AP classes..when I was in high school in the late 70's, my school offered I believe 4, and they wanted to drop them because they only had 6 kids who wanted to take them..).
Kids haven't fundamentally changed as much as the world changed, they don't have dear old dad the way I did who was home for dinner and after dinner we did things like work on cars, mom is working, and they certainly don't have the free time I did growing up. The image of the slacker kid playing video games, or on facebook, or whatnot, is just that, these kids are doing a lot more than we did. The other thing was that by the time I was growing up trains were not a 'big item", either, and by middle school even if kids had them younger it was pretty much a tiny handful of kids, by high school it was near zero......and all I can say is that when I read the articles about the guys with the layouts in OGRR and CTT, the routine is they dropped trains as a kid, and then discovered them as an adult, and I think that always has been true, this is now an adult hobby, not a kid's toy. The fact that the manufacturers today are a lot more concerned with hi rail/scale is an indication of that, kids to be honest don't care if an engine is scale sized, if the rivets are correct, if the chuff is right for the prototype, they always cared about running the trains for the most part.
I also question the idea that somehow interest in model/toy trains is influenced by exposure to trains, since many of us in the hobby today, people my age (mid 50's) and younger, never experienced the 'golden age of trains'. I never saw a steam engine in service, I never rode a long distance passenger train (I did ride commuter rail, but that is different), and by the time I was born airline travel and the car had already pretty much doomed passenger service...yet here I am, and many others on here. I think the hobby is going to change, as it already has, the day of it being dominated by people running post war in conventional mode is going to change, the future likely will be command control as it evolves, and it will likely be a smaller hobby but it will exist. After all, MTH and Lionel and Atlas and so forth are making money on new products, and the market for them is already a fraction of the total size of the market, given how many of us run only post war or only buy stuff used, and they are staying in business. I think there will always be people running post war for nostalgia sake, but I think what is today the 'new market' is going to be most of the hobby going down the road.