These children were mostly railway workers' kids. Whole purpose of it was to teach them railway jobs were cool to make them follow their parents' steps.

In the Soviet Union, and to a great extent in Russia till now, railway system is very independent from the State. It's frequently called a state within a state. It has it's own power stations, construction departments that build among other things, housing for workers, their own hospitals and even their own medical schools, it's own police, their own hotels and Black Sea resorts for workers, in the Soviet times they had even their own Gulags. It's a closed-loop system largely independent from the rest of it. So they have their own take on schooling, too.

Happened that way because after the Revolution of 1917, the state largely collapsed and was unable to do shit for at least next 6-7 years. Railway had to figure out how to work on its own.