The types of roads children bike on, and the types of roads adults would like to bike on have different risk factors. You've said it directly in your comment: t

The types of roads children bike on, and the types of roads adults would like to bike on have different risk factors. You've said it directly in your comment: these children are biking on suburban streets. [0] At least from my experience, suburban streets have much less traffic, and what traffic they do have is usually slower. On the other hand, the types of roads adults would need to use to commute have much more traffic, and at higher speeds. [0] - An interesting study to do would be to compare the bicycling rates of children in suburbs vs those in urban/downtown areas. I suspect that the rate in suburbs would be significantly higher.