Hi Caraleigh,
It is good that the care team is on top of things ordering PT, bone scan and such. Prednisone is not talked about a lot but it is actually a recommended treatment early on, so good to see that too.
I second the pool suggestion. It has helped many of us and kept me in shape and is where I started walking again. It is also fun! The PT may not seem to have done much but sometimes what you are accomplishing is prevention of further loss of muscle and function. The gains can sometimes appear as neutral.
Brain plasticity is in your favor. I would suggest working on tolerance and recognition of stimulus. When there is a lot of pain in the skin this can be challenging but starting with soft cloth, moving to rougher, using nylon brushes, etc on a daily basis can help nerves remember what they are supposed to do.
Pay attention to when things feel better and worse. There is sometimes a push to hurry up and get better by overworking the area. This can lead to flare up and setback. Recovery with CRPS goes slowly and should be undertaken with care and mindfulness. Try to figure out activities that increase pain and back off from those, then start up again slowly. I must've done this a hundred times in order to walk again.
Trust your wisdom and instinct. Doctors and imaging aren't always accurate. It may be something is irritated in the foot that isn't showing on MRI. This does happen. If laying off regular activity seems to help your son, maybe revisit treating him he has like an injury for several weeks, especially if activity was never modified much. Just a thought....
Glad to see you are getting counseling. It is scary going through this and support is great. There are therapists who specialize in pain and use modalities such as hypnosis and EMDR (eye movement desensitization reprocessing) both of which I tried to very helpful effect. These can both be done with children.
Keep fighting and maintain hope. Dr. Stanton-Hicks of Cleveland Clinic says 80% of people improve over time. Odds are in your sons favor.
Sending hugs and healing love,