Step - I am glad you got a second opinion... what you are says sounds like a hypermobility issue. I suffer from severe hypermobility and unluckily for me it wasn't picked up until I was in my 20's. By then the damage that had resulted from repeated soft tissue injuries meant that physio wasn't any good for me. Luckily for your son it has been picked up early and early intervention and exercises will give him the best opertunity to develop more stable joints and therefor less injuries when he is older and less long term problems.

My sister was picked up much younger than me and her joints are in much better shape because of this.

Doing physio exercises with a little one can be very frustrating and tiresome but the benefits are so worthwhile that I wouldn't ever skip my DD's exercises. Personally I have had surgury on both knees and 5 ops on 1 ankle. I also have arthritis in most of my joints. The worst thing for me was that during childbirth I dislocated both hips and have had many sublaxations (partial dislocations) since that have needed medical intervention to correct them. All this aside, if my 'loose' joints had have been picked up and addressed as a child I would not be in this possition now.

If your physio thinks it may be something more they will have more sway with getting the doctors to take any action that is required.