In a perfect world yes! However in the real world compartments are a practical solution. However if one is paying what is now quite a bit of money for a ticket, I kind of expect a compartment to myself.
Now someone will no doubt say this is unreasonable. Fine - in which case there's a high likelihood I simply won't bother travelling. Unlike the proper network where people may well *need* to travel from A to B, heritage railways are very much a choice. If people experience a day out from hell then they won't repeat it again, which will represent lost income, taking us back to heritage railways struggling.
I can see where you are coming from.
Personally as someone who has spent over 33 years teaching other people's children, but who has chosen not to have any of my own, I do like to escape their presence. I however, I do recognise that today's youngsters are potentially tomorrows enthusiasts and volunteers. It is not only children who can be annoying though it is sometimes parents who don't realise that they are the adults and should set an example and expect their children to be have. Some years ago I travelled up the Snaefell Mountain Railway with parents who were interacting with their teenage children as though they were teenagers themselves. Wasn't a pleasant experience.
What we really need is for more heritage railways to offer first class to those prepared to pay a bit more and quite often, though not always, escape the children.
Unfortunately in recent years there appears, as on the national rail network, to have been a decline in First Class provision. The Ffestiniog Railway for example used to have first class accommodation located around the train with a choice of compartments as well as the observation car. However, in the last three years or so only the observation car option is available.
Llangollen Railway used to offer first class - but that appeared to fizzle out many years ago. Tal-y-llyn still seem to offer it on most trains, but I think G&WR have now phased it out.
My other passion apart from railways is ships.
Due to the fact that the nearest shipping routes to my home serve the Isle of Man - I, and several other local enthusiasts, have chosen to be members of the Executive Travel Club due to the fact that no children are allowed, there are free sandwiches and drinks - including beer! I have been a member now for over 20 years.
It is rather good and offers what you want but in a maritime context!
John