I rode my bike to school since I was 4 years old, over a rural way with 50 miles an hour traffic. My older sister on another bike, and my mom with my younger brother on the back seat. Key is that the adult cycles further into the road, with the child cycling between the adult and the curb, effectively occupying the whole lane. Of course, all that combined with good high viz jackets and lights. Your child should quickly enough understand the importance of staying next to you and not speeding away.
