I remember when our twins were infants we lived in a third floor walkup in Greenwich Village in New York City. One day I decided to give my wife a break and take the kids out for a stroll in our neighborhood. With twins there is a certain amount of baggage required when you head out the door. Stroller built for two? Check. Diaper bag with snacks and so on? Check. Bottles of formula and other necessities? Check.

Carrying two, active ten-month-old babies and navigating down the stairs with all that stuff was, well, it wasn’t actually possible. I was beginning to grasp this as I stood on the stoop looking helpless and trying to figure out what to do. Should I put the kids down and unfold the stroller? That didn’t seem like a great idea. Should I go back upstairs and leave things on the landi…