It was a nasty spring day in Duluth. Another of those surly east-wind jobs that we know so well here in April and May. Forty-two degrees, and the sky leaking badly.

But the yellow dog and I needed a walk, so I layered up in fleece and rain gear. We headed to Hartley Park in Duluth's Woodland neighborhood. It's 660 acres of woods, waters and - this time of year - spring peepers a-courting by the hundreds.

I'll admit I was feeling a bit irritated by the weather. It had been a long winter, and this icy rain seemed like cruel and unusual punishment.

And then I heard them. Not the peepers. The pre-schoolers. Hartley Nature Center operates a nature-based preschool in the park, and, sure enough, a gaggle of these 3- to 5-year-olds was up in the pines having a grand time. I could hear them laughing and hooting and hollering.

I had no idea what they were doing, but they were clearly happy. Then I saw a knot of them. They were crawling around on a downed tree, hopping and clambering and jumping and sliding and falling down and getting up. They all wore rain gear - vibrant blues and lavenders and pinks and lime greens. It looked as if the forest floor had sprouted neon mushrooms.

How about that, I thought. Here I was thinking this was a dreadful day to be out, and these kids were having a good ol' time, and no doubt learning something in the process.

All of which gave me great hope that these young sprouts from the newest generation are learning to appreciate and value the natural world around them. I am happy that their parents suit them up in the right gear for such adventures - no small task. And I'm glad that Hartley Nature Center - and other nature-based preschools in Duluth - offer these experiences.

Later, I asked Kaitlin Erpestad, preschool director at Hartley, just what those kids were up to.

"What you saw was free, unstructured nature play," said Erpestad, a Duluth native. "They play with sticks, build forts, play in the mud, climb trees, roll down the hill, make mud pies - all of the things we think of from our childhood."

In the rain. In the wind. In the snow.

"We go outside every single day," Erpestad said. "We haven't missed a day outside in five years."

Through that child-directed play, those little mushrooms are learning.

"That's the beautiful part," Erpestad said. "The free, unstructured, child-led play is preparing them for school, developing their problem-solving skills, their creativity, their communication skills, their ability to assess and take risks. They're developing a sense of wonder. It's much more than it seems like to someone passing by, seeing them playing in the mud."

I thought about my own childhood. We didn't have nature-based preschools like the one at Hartley Nature Center. Then again, we didn't have smartphones and video games, either. What we had was freedom to roam the neighborhood, finding our own unstructured play. We built forts and tree houses. We created little towns in the dirt. We rigged ropes and climbed on them. We made little ramps and rode bikes off of them. We climbed trees. We fell down. We got up.

We didn't have someone like Erpestad running the show. We had Mom.

"You kids go outside and play now," she'd say, shooing us toward the door no matter what the weather.

I remember on rainy days sending twigs down the miniature rapids in our gutters, watching our "boats" careen and dance down those raging rivers as my brother and I trotted along beside them. I'm not saying that led directly to paddling rivers to Hudson Bay 30 or 40 years later. But something must have lodged in my gray matter while I watched those little sticks buck and lurch along.

I keep thinking about something else Erpestad said about those preschoolers when we talked.

"One of the things we do," she said, "is let them be kids in the woods."

What an amazing concept.

Sam Cook is a freelance writer for the News Tribune. Reach him at cooksam48@gmail.com or find him on Facebook at facebook.com/sam.cook.5249.