I see them once or twice a week, and most of the time, they're just calmly getting the kids on and off the train, each with their own tiny backpack. Mom hands out little ziplock baggies with breakfast treats. One morning it was pancakes. Sometimes, they all get off at the same stop, sometimes dad takes the eldest one direction and mom the younger two another.
The first day I really noticed them, the eldest got his backpack strap stuck in the bench at the subway stop. His mother was furiously trying to pull it out, as the father stood holding the subway door open and keeping the two younger ones inside the car. Finally, she pulled out a small knife from the pocket of her coat, cut the strap free, and they both ran aboard.
A couple of weeks ago, either mom was sick or away and dad had to wrangle all three. I did not envy him ... Three small kids, subway changes, three backpacks, hats, coats, etc. He did it though, like a million single mothers and fathers do every day. There weren't any little baggies that day, though.