Ride with traffic. Make your own decisions. The specific safety issue for children change dramatically by age and the kind of environment they are riding in. The are taught balance, steering and pedaling. They need to keep their speed commensurate with their skills.
Child starts to leave court or driveway, to use walkways.
He or she starts to encounter pedestrians and hazards like cracks in the pavement, glass, debris, poles, benches, etc. Cyclist start to speed up. Most accidents don't involve motor vehicles. Most are falls, collisions with stationary objects, collisions with pedestrians or collisions with other bikes. While accidents with cars are statistically small, procedures for entering the motor vehicles merit extra practice for beginning cyclists.