Outside provides the necessary details:
A long row of pre-school-aged kids, aboard low-slung bikes with no brakes or pedals, takes off from a start ramp like a pack of greyhounds. The kids kick their bikes up to speeds that would make most adults uncomfortable, and carve through the course’s maze of sharp corners with tenacity and grace.
A few kids don’t make it. They splay out across the track in a pile of elbow and kneepads and full-face helmets. And then, there’s one kid, coming from behind, who executes a perfect pass on his recently potty-trained competitors and crosses the line first, his chest forward in an elated victory celebration...
Today, anyone who's serious about teaching a kid to ride at an early age will likely eschew training wheels in favor of a balance bike. Dozens of different companies now sell them, including every major bike brand. This transformation in kids' bike technology has led to an entire generation of toddlers who rip on two wheels.
Among my group of dad friends in Austin—roadies and mountain bikers who might pull up their Strava feed over a pint of beer—the kids who start out on balance bikes often master cycling at a mind-bogglingly early age. One buddy’s kid switched to a pedal bike at just two years old, and was churning out 20-mile rides by three.