You've done a nice job making your plan look good with SCARM. You've met your objectives of using your current inventories of different track and incorporating certain accessories on a 4x8 (?) platform.
There are some overly close clearances with buildings and tunnel portals and other
features, that need to be adjusted to make the plan operable. It doesn't really fit as-is in a 48" x 96" space.
Construction is somewhat complicated by the congested 2-level configuration. It's basically two disconnected ovals and I think the operating fun is rather limited with that.
Since this layout is intended for your young son, I suggest that you keep it all on one level so it is easier to build and easier to change around. Your son will get more out of it if he has freedom to change tracks around and put buildings in different places.
Thortrains.com has lots of suggestions for smaller layouts and you can search the OGR archives for additional ideas.
Good luck !
