Layout for Your Families' (grand) Kids

Unless we get the next generation involved the hobby will die. 

The layout I built in in the 50's was for kids and by kids (me and sib's; no parental involvement). The one I built 35 yrs later was for and built with my son. 

Layouts now appear to be built for and by an older generation. Very Different. I suspect that most of the current layout builders are empty nesters and the only in-family kids available are grandkids.

I am building and operating a layout for/with grandkids (4: 5-14). My current thoughts on making the process and the layout "for kids" are below. I'm writing this to get others' views and experiences on the subject. Holding today's kids' interest is hard - let's share what we know. 

Goals:

1. Creating a layout that the kids want to play with for hours, unsupervised, frequently.
2. Having an activity where the kids can really engage with grandpa (grandma if she is the/a train person)

Challenges and differences 

1. time available (unless they live in your house or next door, you get less of your grandkids time than you had for trains as a kid, or you could get with your kids in the house). 
2. seniors vs kids on detail, attention span, complexity of scope,
3. If multiple kids, age span
4. skills and equipment (tools)  that grandpa has vs what I had as a kid
5. (frequently) boxes of old gear
6. money (You probably have more money available for this than you did as a kid)

Some Concepts 

1. You are trying to building something that will hold continuing interest of your grandkids, not something for a one-time experience at a train show or Christmas open house for visitors.
2. My experience is that it is harder to get them involved in building rather than in running. Building is slower, and we seniors are more deliberate at it than kids. You probably can get resident kids deeply involved in building; frequently visiting grandkids, not so much.
3. So, get it actually running soon, and almost always running (a long, not-running build period is NG; long down times NG)
4. Kids-height table (30"). moveable foot stool for the little ones
5. everything reachable by them (max 24 in reach)
6. impossible to run a train off the table (removable clear barriers, which also let you control the access of the little fingers of the littlest ones)
7. everything must run correctly and reliably (big conflict with old gear)
8. Nothing that if they (mis) handle it you will have a heart attack
9. They (or you) can run in demo/loop mode (show and tell for visitors), and an evolving "real" operation mode
10. Real operating mode needs to be able to get complicated enough to hold their interest over the years. For me this dictated a minimum size, and other aspects of the layout
11. Obviously, kids run the trains, not you.
12. kids like throwing switches (turnouts)
13. kids like operating accessories and operating cars; have plenty, let them operate them
14. automate less: it's better to having a crossing gate controlled by a switch they have to remember to push, rather than triggered by the presence of a train. Remembering in time is part of the game.
15. Scenic realism seems not important to most of the kids. 
16. kids like to move vehicles, people and animals; let them
17. Kids like lights
18. Kids like things named after them and also given familiar names (towns, industrial and commercial buildings, schools, etc.)
19. kids love rolling, very height-adjustable stools/chairs. (Perch to view)
20. kids love mechanics' rolling creeper for under the table
21. for little ones, have other toys nearby when attention flags
22. It helps if every time they come something has been added or changed

If there is interest, I can follow with more experiences and what layout has resulted so far. I'm after input.