My 5 1/2 year old son is very much in to trains (as is my 2 year old, although it is all about Thomas for him.). My dad always has a Christmas layout for his grandkids and my father in law is an engineer for a steel company who works on railroad overpasses and bridges.
Christmas 2005 my father had a train table built by the local hobby store. It was on a 4’ x 7’ sheet of plywood but too big for my dad to use. He gave it to my son with a Lionel Penn Flyer RTR kit. My son has loved playing with the trains ever since.
Christmas 2006 we gave my son the Lionel Santa Fe freight train set, RTR. We had two trains (one steam and one diesel) running on two independent tracks on the 4’ x 7’ layout (this is in O scale by the way).
I decided we needed more room. The train table is in our garage so there is a decent amount of space. I got a 4’ x 8’ sheet of plywood, constructed the underside (benchwork I believe it is called) and attached it to our existing 4’ x 7’ table (which sits atop an old kitchen table, so there was no benchwork involved with it).
What we now have is an 8’ x 7’ train table for our O scale trains. After much research on how to set this up with the best use of the space available, we came up with the following.
Keep in mind this is done to the desires of my 5 year old, therefore, there is no continuity with the rail lines, years, etc. He prefers freight cars, so that is what he has. We have two trains running on independent loops using two transformers. There is some track put down that goes no where (other than under the girder bridge) because it does indeed go no where - we hope to add a trolley type car to this line in the future. My 2 year old would love to add the Thomas trains to the layout, but so far that is not going to happen.
Next up is to add some scenery, etc. to a pr
He’ll probly have hours of fun on that. I know i would 
After few trees and scenery it will start looking even better. You maybe could add a station or something or Small depot.