I got one last hug out of my son before he headed off to bed as a tween for the last time.

He humored me, but as I wrapped my arms around him, he rolled his eyes and said, "I'm not going to feel any different tomorrow, you know."

As if that was the point. Right then, it was all about me. How can I be old enough to have a teenage kid when I still vividly remember him as a baby? I can still picture the ultrasound of this stubborn child nine days after his due date — so big that we couldn't see much more than his spine and the knees positioned modestly to conceal his private bits, which meant his gender remained a surprise until we finally forced him out of the womb two days later with a Pitocin drip.

Burned into my mind is the cover of the book I brought to the neonatal intensive care unit with me every day for a week while my son recovered from pneumonia. It was "The Cunning Man" by Robertson Davies. Despite all the hours I sat in an uncomfortable rocking chair next to my sleeping newborn, I didn't finish reading the book until after I'd taken my son home because I couldn't read more than a few sentences at a time before looking up to see if that wondrous newborn was awake so I could take him into my arms.

When he was finally healthy enough to nurse, I can still see the surprise and delight on his face as he ravenously drained me, thus initiating a series of demands that have changed with his needs and interests, but maintain the same level of impatience and intensity to this day. Our lives are very different than they were 13 years ago. For instance, we now seem to be moving at warp speed, the only reasonable explanation for how so much time has passed.

But other things are just the same, like my son being the same driving force in my life he's been since the day I discovered he was on his way. He's inspired me creatively, academically, professionally and, of course, maternally as well. His little sister is part of our lives because my son taught us that the joys of parenthood far outweigh the challenges (something I often need to remind myself).

Each time one of my children reaches a milestone, someone inevitably says, "Enjoy it while you can because it's only going to get harder." And if I've learned anything over the past 13 years, it's that it's true. It gets harder, almost by the minute. But those minutes fly by so quickly and even when time seems to grind almost to a halt during a moment of crisis, once we're through it I discover that no considerable time has passed at all and we're on to something else before I can even catch my breath.

Of course it's going to get harder, but that's not what matters. If 13 years can feel like a nanosecond, then there's no time to waste worrying about what's going to happen because it's much more important to make the most of these fleeting moments.