With a child of my own interested in running a marathon, I researched marathon training programs for youth in the US (there are some!), injury rates and how these compare to high school running programs.
My guess some of the lower injury rates with endurance training with youth is the emphasis is on volume and not intensity.
In my son's case, he been practicing longer runs for a year before he tried a marathon. The base training did seem give him going to a formal middle school training program later.
Now he's sophomore and has good success in the school running programs without major injuries.