Does he see a physical therapist? I am a PT and groin pain can result from dysfunction in the hip. It can be caused by muscle tightness, a tear in the labrum, improper biomechanics of the joint caused by an abnormal gait, recent changes to gait due to growth, or even a foot problem such as a collapsed arch which might change the mechanics of his gait. An evaluation may be worth your while because it may be something as simple as needing orthotics for his shoes or some stretches. Try to take note of when he has the pain: is it always in standing?, at rest or with activity?, if with activity which ones?, what position does he sleep in?, does it wake him at night?, did he have a fall, slip or trip of some kind before it started?, is it on both sides or only one? etc. things like this can help the therapist determine what might be causing the problem. Hope this helps!