Surgical remedy may be in his future but he is young. Let an ortho MD determine that, particularly a pediatric one. Yes I would assume that the ligaments in the anterior/inferior aspect are loose/stretched. What you worry about with excessive motion is tearing other things as bones move where they are not supposed to. Tough one . Let a sports ortho decide then the decision is in the professionals hand/court/etc. This takes the guesswork out of it for you and you will be following informed medical advise