My perfectly healthy kid, sitting on the exam table in his soccer jersey, was dumbstruck. So was my wife.

Our doctor’s warning — one he now gives to all his young patients and their families — came from his years of caring for an increasing flow of kids suffering serious, sometimes life-altering concussions from playing soccer. “If I don’t get this information across,” he told me, “even at the risk of upsetting people, I’ve failed. I haven’t done my job.”

According to Dr. Robert Cantu, one of the country’s top specialists in youth sports injury, soccer is right up there behind football in the incidence of reported concussions in kids. The Centers for Disease Control estimates that about 10,000 kids land in the emergency room every year for soccer-related brain injuries.

But at the same time, following the doctor’s orders seemed unthinkable.