Beth. I was 65 when I had a AVM removed from my left cerebellum in 2016.i also lost short term nemory and I did 2 years of Physical Therapy, Occupational Therapy, Cognitive Therapy and also therapy for eyes, ( I have double vision from the surgery)
What worked for me to help regain my short term memory was constant book reading. It took roughly 1 year before I started to remember what I was reading and also remembering tv shows that I watched.
I fully recovered except for the double vision in 2019.
Your son is still young his recovery might be quicker. I suggest reading, talking to him and asking him to repeat back what he heard. It is a long recovery but hang in there, it does improve.
Michael Barber