Curious if anyone has any experience with this game. I would like to get it for my 8 year old son but I am somewhat concerned the economic level of the game may prove too much if the control of it isnt simplistic enough. The building aspect seems great, an easy tool. An economic interface with numbers and simple controls to buy/sell would be perfect. I think once we get into forecasting, charts and graphs he would lose interest.

There are no forcasts, charts or graphs. But actually it would be nice if there were.
This appears to be a economics/transport simulation first. So a lot of planning ahead is neessesary. And the documentaion is lacking/non-existant.

There is also no sandbox mode (at least I found none). So it might not be the right game for a 8-year old.

Well, thanks to the modding community, which is mainly German (surprise, surprise!), there are ways to remedy that. I'm surprised there's not an official option for that though. Anyway, the two mods that are useful for that are the 'Cost' and 'Timeless' mod scripts that can be found here. The first will allow you to set all prices to zero, and the second unlocks everything.

I'm not one for kid-friendly games, as my first PC game was Transport Tycoon at 10 yo. But Train Fever would be probably frustrating for such a young age, because in addition to transporting like in Transport Tycoon, you also need to check the city zoning and plan accordingly your passenger transportation, your industries might suddenly drop all or a large part of their transportation with your company, and also there is the never-explained 20 minutes time limit that applies to anything you transport.

All in all, it's like Transport Tycoon made more maddening/difficult. I suggest children should just start with Transpor Tycoon/Locomotion/Rollercoaster Tycoon, it has wonderful pixel art and music and the trains are cute specifically because it doesn't respect real world scale, looking like a toy trainset.

I love the Timeless Mod, it takes away the ageing of engines and let you run them forever. This change alone takes away all the pressure in the game. I can imagine it is a nice brainteaser to get the train tracks right, the building tool can be a challenge at times :)

There is no specific sandbox mode, but really the game is sandbox by design there is really is no set goals other than not running out of money, and I could be wrong but I'm never sure there is an actual end date. That's basically what a sandbox game is.

Also I would say the game is kid friendly, but may be a little difficult for a child to figure out completely.

True Sandbox (as I use it) means the lack of resource management.
By default the games does not have this.

However, there are mods that can remove the resource management and time limitations on vehicles.