Ed, This is a great topic, and one very important to me (although from the viewpoint of a parent rather than grandparent). You've amassed a great list of thoughtful observations. I do have some thoughts on #6 though.
6. Imossible 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).
Over the years, I've read this a lot on the forum but it's a big mistake. For kids to develop a strong interest in this hobby, they need the same unrestricted access to trains we enjoyed as kids.
An inspirational, kid friendly layout is one where little fingers can freely explore and make mistakes... even big ones that cause the loco to smash into the floor. Things will break and that needs to be OK. This is how kids learn.
When a boxcar finds its way into the hands of a three year old who is perfectly content with rolling it around on the floor, it's time to grab a caboose and join him!
