I remember talking to Sawyer after a long expedition in the subarctic. He was still in middle school. "I can't talk to my friends about the trip," he said. "Whenever I start to tell them about it, they say, 'Oh, yeah, I went to a hunting camp with my dad last fall,' like it's the same thing. It's not their fault, but they just don't get it." When he said that, I ran the image of my son, barely 100 pounds, toiling across a two-mile-long muskeg portage, dwarfed by his load, waving black flies out of his face, 20 days into an expedition that was only halfway over. "Yeah," I said to him. "It isn't their fault, but you're right, there's no way they can relate."

There's another benefit -- the lessons and insights these three children teach me in these experiences.

I'll never forget watching Eli explore the texture of warm sand for the first time, before he turned one. Sawyer finding a mud wallow in a riverbank and going full-body immersion, and convincing the rest of us to join him. Ruby playing air guitar by a sputtering fire on a drizzly, hypothermic day in the Far North. The games they invent, the treasures they find, the questions they ask, the observations they make, the fortitude and joy with which they embrace the experience. More than anything, the lesson for me is that, from the get-go, they have been absolutely unfazed by being in wild places. They never for a second have questioned it. In fact, as they have gotten older, they keep raising the bar.

Here, on this alpine day, before we summit, we seek the literal headwaters of the Yellowstone, that first drip of river off the snout of snowfield, the river we have come to know intimately as a family. Ruby forges out ahead of the pack, disappears around the shoulder of a ridge, hiking fast. The boys scramble to catch up with her. Marypat and I pick up the pace, trying to keep up. There is something ineffable, enticing, mysterious about the source of a great river. The lure is primal, universal. It has to be close. Around the corner, the low, gentle divide separates the flow. A small snowfield is pasted against the steep talus slope. At the base, water drips off in the summer warmth, filling a shallow basin, trickling across a bedrock sill.

Then I see Ruby.

She is sprawled on her belly, her face over the icy water as if studying her reflection. Her lips are pursed, she drinks deep, filling her belly with the first drops of this storied river. We all follow her lead, one after another, lining up prone on the sun-warmed rock in this high country that is so thick with bears, drinking the river that carried our boats across the plains of Montana. It is absolutely the right thing to do. Ruby may be barely out of elementary school, but she knows unerringly what is called for in this wild moment.

The day at the headwaters, and scaling Younts Peak, is long. The kids discover glissading on our descent from the lofty perch on Younts. The same snowfields we had carefully kick-stepped up, they schuss down on their boots, whooping and giggling. And all the way back around the headwall, they scamper up every little snow bank for more. Fatigue? What fatigue?

Around twilight, we make it back to camp and have dinner perched near a small lake. After dinner, they all head to the far side of the lake to another small snow patch. They strip to their undies and camp shoes, then start yo-yoing up and down the slope, each run ending with a bracing splashdown in the shallow lake. Then, in the gloaming, Sawyer and Marypat walk together to a nearby knoll to study the peaks and ridges that seam the horizon, with the Tetons floating in the purple distance.

A full moon rises. It is absolutely silent. Only the hum of the earth, the hum of summer, and the grace of pale light pooling in our high camp. I think of what my adventures used to be like, without the kids -- and how Marypat and I might have kidless adventures again after they grow up and leave us. And I see, clear as the moonlit beauty of this evening, that it has never been about what we have given them. Instead, it's everything that they have led us to.

Alan Kesselheim is the author of 11 books, including two in 2012: Let Them Paddle: Coming of Age on the Water and Montana: Real Place, Real People. He lives with his family in Bozeman, Mont.