“Dad, go ahead,” my twenty-year-old said, gesturing towards the castle’s stone spiral staircase with one arm. My husband could not fully see the gesture as he began his way down the steep, narrow turns. But I saw it: a gesture that not only invited his father to precede him but also signaled a kind of watching-over of the man who was wearing a knee brace this summer.

“What?” the boy said to me, catching a glimpse of my face as he followed his father.

“Just thinking about how things change,” I said.

And it was all I needed to say for this sensitive first-born of mine to understand precisely what I meant. I don’t know if he remembered in that moment the same things I did, but the feeling of them all—the climbing structures and playground forts, the tricky places on hiking paths, the icy sidewalks and wobbly bridges and high fences, the trees and railings and wall-tops, the staircases of every description—was surely there. All those high, precarious, slippery, new places he climbed and scampered along and wanted to explore as a little guy, when we said, with our words or our bodies or both, “you go first, and we’ll follow and steady you if you slip.”

I could still see his chubby baby self, his rosy cheeks and small sturdy legs, his striped t-shirts and little windbreakers and tennis shoes that closed with velcro. It doesn’t seem so very long ago that I was dressing him. That he was scrambling through adventures until he would collapse exhausted on my lap, where I could relish the smell of sunshine in his hair.

In the place my children always called the “brown playground,” with its enormous wooden structure full of narrow turrets and bouncy bridges and rope nets, I spent several summers trying to jam myself through narrow openings meant for five-year-olds, trying to follow my curious toddlers through places where they might need help navigating steps that were too tall. I am sure he could not remember those days, before he could even talk, when his urge to climb drew him to challenges meant for the big kids. But I am equally sure that the feeling of a hand waiting to catch him should he stumble was still with him.

Every single one of those days hung there in the air between the two of us in that moment on those castle stairs.

He looked back at me, his expression full of everything I was feeling…the march of time, the shock of realizing how suddenly and how softly the child can become the protector. His smile was gentle. An embrace for me.

“Yeah,” was all he needed to say. And then started down the stairs to make sure his father did not stumble.

I’ve been thinking about that moment a lot in the last week, as we packed up and moved his little sister several hundred miles away for the start of her first year in college. Walking past the emptiness of her bedroom produces a gasping reaction as if I’ve been socked in the stomach. It’s only been two days, and I suppose I will get used to it.

He told her as he hugged her goodbye that she had to text him, to call him, to give him a tour of her room. To keep in touch.

Out of nowhere, yesterday, he said to me, “I’ll try to come home a bit more this semester.” (He lives on campus, but is in college in our town.) “I’ll come home for dinner once a week. I can make time for that.”

When I said I knew he’d be busy, and I would understand if he couldn’t, he said, “no, I will. It’s going to be really weird for you guys.”

It was the third or fourth time this summer that I’ve found myself realizing: somehow this boy of mine has become a man. One who looks out for all of us.

I am sitting here today, on the eve of moving my ninety-five-year-old father-in-law into a care facility, and thinking a lot of inchoate thoughts about time and cycles and generations and the directions in which care flows.

It is heartwarming, of course, and also a little destabilizing to realize that little by little this is what happens: your children begin to need you less, and you begin to need them more.