That was a quick result - I put in for a change of circumstances at unfortunately, the same time as renewal.. last august. I am still waiting for an assessment!
Your application should state:
What dx, medication etc.
What the applicant cannot do - and link that back to the various issues for EACH question.
Assume that each question is a stand alone, that the person reading it has not read the previous questions and will forget the answer to this one immediately before they read the next.
So using me as an example for the moving around question:
Widdlin' cannot stand and move without her wheelchair without experiencing severe pain, debilitating breathlessness and falling. If Widdlin' attempts to stand or move she falls. This happens every time Widdlin' attempts to stand and move.
SO then when it comes to say personal care, bathing etc - I'd repeat that bit as well, I would not assume they have taken that part into account, they won't.
So I would have to explain that I can't get in the shower, as that would involve standing, which I can't do.
It's really bloody tedious.
Find the list of points and what criteria they're awarded for - remember that it is not sufficient for the person to do something - hell, I can haul my ass up the stairs - they have to be able to do something safely, without pain, in a reasonable time frame - I haul my ass up the stairs on my hands and knees twice a day (loo midday, bedtime), it isn't safe, I fall frequently and it hurts a shitload and takes ages. But im waiting on a DFG, and I won't shit in a bucket.
The point of that is - there are things you/the person involved may be forcing themselves to do now because there is no choice - that doesn't mean its acceptable, it doesn't mean they're actually capable and could be considered able to do a thing the same way a non-disabled person can.
Once you've got the list of points the report you have can be used to pick out whats wrong, what they've missed or misunderstood - and formulate your written MR (never do that over the phone, submit it in writing!).
That way you can hit the specific key points/terms they want to see for the applicant to meet that criteria.
You don't say the age of your son - it is possible they're deeming the level of care he requires to be similar to the level of care a non-disabled child would require, so really spell out HOW it is different.