I learned about gravel the hard way, when I was twenty. I biked into a sharp turn off a busy street at full speed. There was gravel there and I went down hard and fast. Bam. No one was there to give me a hand up. Fortunately, the intersection was empty at the moment.
My kids started going over the handlebars much earlier. They were crashing push bikes before they had pedals. My daughter learned about gravel on corners at the sidewalk corner in front of our house. She learned about the danger of fast descents going over the bars on a grassy knoll at the local park. A lone rock on a greenway at age four sent her over the bars again, re-affirming the value of her helmet. These were all hard to watch as a parent, and certainly not intentional lessons.
But by age 10 she had a decade of experience of riding on bikes or in bikes. Hard lessons when behind her when the stakes were lower. We trusted her to bike home alone the three 3 miles (5km) from downtown by herself. She braked on the downhills. She slowed for the corners. She looked for gravel. She stopped and looks for cars at intersections.
Now she's 14 and e-bikes to babysitting jobs while also looking forward to her driver's permit. I can't think of a better way to prepare my child to get behind the wheel then the path she's traveled. She will have already spent a decade and half as a vulnerable but increasingly independent and experienced road user.