This past Sunday I spent a good portion of the afternoon with my newest nephew in my arms. I and my own kids were at my sister-in-law’s house for a celebration, the little guy was understandably unwilling to have to entertain himself at his own party, and I was the only adult around who wasn’t occupied with cooking or some other preparation. I didn’t mind, of course—he’s a sweet kid who smiles easily and has adorably squishy cheeks. More than that, though, it’s been a while since any of my own children were that small, a fact I’m aware of all the time.

Of course, when my father-in-law arrived and told me “That looks good on you, maybe you should think about having another,” my response was to say “Bite. Your. Tongue!” I later told my mother-in-law, truthfully, that I had just been thinking that morning how thankful I was not to have a baby right now.

I’m going to be thirty-nine next month, which is to say that for about six months now I’ve been saying “I’m almost forty.” I love my children, sometimes so powerfully that my breath literally catches in my throat and I feel like I might die from it. But the idea of being almost forty and having a newborn, having all the same midnight feedings and burpings and changings and desperate entreaties to please, just this once, just go to sleep, just give me three hours, just two, having all of that and also my almost-forty knees and my almost-forty back, and three other kids on top of it all... Well, it’s more than either my wife or I want to deal with. We decided a long time ago that three would be it.

And yet, as thankful as I feel to see my youngest out of diapers and writing her and her siblings’ names (on every loose scrap of paper that she can get a hand on), to say, aloud “I am not having another baby” is not without a certain pang, a certain feeling of loss, of grief. Holding my little nephew, I feel the weight of that decision more than I feel the small weight of his body.

Not that this is a new sensation, though perhaps the direction is different now. Four years ago, when we told our son that he was going to have another baby sister, he cried because he knew he’d never get to have a little brother. He loves both of his sisters now; he’s a great brother. He still sighs from time to time about the brother he wished he could have known. Sometimes I sigh about that, too.

What I’ve realized, though, is that what I’m mourning now is not the loss of some hypothetical future child, nor even the passing of my own children’s infancy. What I’ve actually lost, what I’m in the process of losing, is myself—the self that has young children. The self that is young enough to have young children.

Ten years ago I was about to turn twenty-nine and already thinking of myself as “almost thirty,” and my eldest was a scant two months from being born. And I was excited, of course, and anxious about what kind of parent I’d be, whether I’d be up to the task. But I also felt the nearness of the end of that period of my life, the period in which people still called my wife and I “newlyweds” or “those kids,” the period in which, yes, I had responsibilities but no one and nothing truly depended on me for life. As much as I looked forward to what was to come, I couldn’t help but mourn the life I was leaving behind.

The obvious truth is that having more children wouldn’t keep me from getting older. I had children. I am older. What’s always been harder to see beforehand is that whatever I may have left behind in entering a new phase of life, I’ve gained at least as much more. Change happens whether you will or won’t; there's neither sense nor use in swimming against the tide. It's time. I'm ready.