In the summer of his sixth year, my son Erik hollered from the front yard one evening, “Hey, Dad, watch this.” As I stood by the front door watching, he hopped on a two-wheel bicycle and rode merrily into the distance. I thought I was watching a miracle.

I don’t remember him ever riding on training wheels. He’d never been on a two-wheeler before that moment. When I asked him about it, over this past weekend, he recalled watching a neighborhood pal, who was a year or two older, and saw that the faster his friend pedaled, the easier it was to stay upright. The rest was easy.

For the next decade or so, it felt as if my son spent every free moment of his life cycling off somewhere if he wasn’t throwing a ball around.

I mention this now because his kind of childhood seems to be vanishing across the American landscape.

The Washington Post reports sales of bikes to kids aged 6-to-17 decreased by more than a million from 2014 to 2018, and a decrease in bike sales over the past year of 7 percent in dollars and 7.5 percent in bikes sold.

It’s a drop, says The Post, “serious enough that retailers have already raised prices to make up for lower demand…and it’s all caused the American bicycling industry — worth $5.6 billion, according to the National Bicycle Dealers Association — to hunker down in preparation for things to get worse.”

To me, this is a reflection of something I notice every time I drive or walk through a residential neighborhood, or past a schoolyard or a sizeable yard or an open field: Kids aren’t riding bikes — and they’re not playing ball.

I don’t mean organized ball, where leagues have been set up by grown-ups and kids are wearing uniforms with sponsors’ names on the back. I mean bunches of kids who have come out of their homes and spontaneously gotten up a game of baseball, softball, stickball, punchball, curb ball, step baseball, three-flies-in, running bases, SPUD, or any of the ancient street games of summer.

Including the game of simply hopping on your bike and riding around the neighborhood — so you could race your pals, or (long ago) catch up to the Good Humor ice cream man, or zip around the corner to get a snowball, or just ride to feel the wind in your face.

What happened to all that childhood joy?

Shall we round up the usual suspects? In my distant youth, when nobody had air conditioning, you were eager to get out of the house to catch some fresh air. Now we’ve got kids saying, “It’s too hot out there.”

Then came round-the-clock TV, and computers, and video games, and all manner of electronic equipment that has so captivated young people that we’ve got health experts worrying about kids’ puffy shapes because they never bother to leave their rooms.

In that sense, the fall in bicycle sales seems part of a modern pattern. But, remember what it felt like to ride your bike down a hill and feel that wind in your face? Now the kids feel it coming out of an air conditioning vent and imagine it’s the real thing.

A former Baltimore Sun columnist and WJZ-TV commentator, Michael Olesker is the author of six books. His most recent, “Front Stoops in the Fifties: Baltimore Legends Come of Age,” was reissued in paperback by the Johns Hopkins University Press.