We had a neighbor and her children and grandchildren (6, 5 and 3 years old) over last night to see the trains, they just left.
I pulled out all the stops, I ran the Thomas set, the 611 passenger train, the 765 freight train, the standard gauge work train with M&Ms in the dump car simultaneously, and had traincam running. I demonstrated and let the kids and adults try the TMCC gantry crane, Mth Firehouse, Gas station, Loading dock, K-line operating milk car, and operating boxcar. And let them try operating the trains conventionally, and with the IPhone and the Cab-2. Those kids were good with the tech.
It was all going on, and they loved it.
I was being barraged with a constant stream of questions and requests, but kept my composure.
It all worked, and nothing got broken: A Christmas miracle in August. 
Now, I am exhausted.
Will these children ever become trainiacs like us, who knows? But, they will never forget last night. This morning I put a couple of recent train mags in their mailbox for the kids. They fly back to their home in England on Monday.
Boomer,
Events like mine and you building the layout may or may not plant the seed, only time will tell. But if the kids are never exposed to the trains, odds are they will never get it. Sometimes the interest is dormant until they have children of their own. You may get a call, “Was thinking of a train under the tree this year, still have that small layout and those trains?”
You have done all you can do.
