That article is weird, for me at least. I very clearly remember when a bunch of kids around the age of six and seven learned to bike, all at the same time. All it took was a woman's bicycle, the old type (I should say "very old" type at this point. Big wheels too), easy for kids. The kids had to stand up, not sit (too big bicycle), and all it took was a single run with someone holding the seat, and letting go after a short while. That was it. No further training required. And that was indeed how I myself learned to bike as well, when I was a kid. Training wheels didn't exist, and are in my opinion pointless unless you want your three year old "bike". For older children it actively does harm.