Responsibility refers here to is transporting actual humans (that will die or will be maimed in case of an accident).

In this sense yes. The phrase "real passengers" can be interpretted differently, more seriously.

But I am not sure the drivers are children. And even if they are, of course not the yongest ones. And if 14/15 year old is allowed to drive after getting trained, it is not a big problem, I think. In some countries 15 year olds can drive cars.

In any case, this railroad is supervised by adults. It is more of an educational establishment.

We have such a railroad here in Minsk. I never cared to visit, even when was a child. Although I briefly knew one person attending it, he was dreaming to work on railroad.