"Hi, please leave me a message ... and I'll call you back."

The voice was very familiar: a boy's voice. I left a message.

A few minutes later, my phone rang.

"Did you just call?"

This voice was also very familiar, but it was a man's voice: a deep, toasty-brown, serious-sounding, grown-up voice. It was, in fact, the same voice as that of the boy on the recording.

What a change a month can make!

On Christmas Day, the teenage boy was still an inch shorter than his elder sister. Just 10 days later, he was an inch taller than she, which among other things probably explained why he'd slept so much over the break.

"Yes! Ha-ha!" the young man crowed. This was a moment for which he had longed all his life. "Bow to me, minion!"

His sister tossed her head, affecting not to mind.

"I'm still taller than you are," she said, "when I stand on my intellect."

He laughed good-naturedly. She could say what she liked: The fact is, he had overtaken her. He could look down on her. Perhaps someday he could even patronize her.

Now we had two proto-adults in the house, along with three other children who seem by comparison still very small, but who are growing speedily themselves.

It is an extraordinary thing, to watch one's children grow up, though I suppose it shouldn't be. Is there anything more normal, after all? A baby grows into a toddler, who grows into a small child, who becomes a larger child, and then an adolescent and finally an adult (there may be stages beyond adulthood, but I find myself disinclined to think of them in this context).

Quite apart from the many skills a person develops on this journey, however, the physical transformation alone is astonishing.

For years, a girl comes down to breakfast. Then without warning -- or so it seems, so quickly does it happen -- you arrive in the kitchen to find a young woman taller than yourself pouring herself a cup of coffee.

For years, a boy's clothes are small versions of what his father wears on weekends: junior-sized jeans and khakis and T-shirts. All of a sudden, their clothes are the same size and thus almost indistinguishable, and this is confusing when you are the laundress.

Parents have tried to capture this journey almost since the invention of the camera, and online you can find a number of charming time-lapse videos of roly-poly babies turning before your eyes into sleek and beautiful children.

My own favorite version of this was the series that once ran in Life Magazine that showed the passage of time on a man and his daughter. In the first image, as I recall, she's just a tiny thing beside her young, strapping father. As the years progress, she grows -- and he shrinks -- until in the final photo, she is the tall, strapping one, and he is stooped and wiry. There is a poignant corollary to all this youthful expansion, which we tend not to celebrate. Funny thing, that.

Meghan Cox Gurdon's column appears on Sunday and Thursday. She can be contacted at mgurdon@ washingtonexaminer.com.