DLA High Rate Mobility for severe mental impairment

Hi everyone, I'm in the process of appealing the DLA decision to drop my son's DLA award from High rate mobility to Lower rate. Currently awaiting the 'appeal bundle'. I'm new to these kind of forums and have to say I like a fish out of water typing this but I'm looking if anyone can offer any advice in this area as I really don't know what other evidence I can provide to support his case. 
My son is 11 years old and has Downs Syndrome. He has always been in receipt of both the high rate care and high rate mobility. I reapplied last year and was told in December that he is still entitled to high rate care but lower rate mobility. I asked for a mandatory reconsideration as I feel his behavior meets all the necessary criteria. ie extreme, disruptive, could cause harm to himself and others etc.
The problem I have had though, I had to submit and old EHC plan from 2017 (Apparently Oldham Council don't update them until they transition to their next school) and so does not reflect his behavior properly and paints and over positive picture of him as he has always suffered from poor muscle tone but slowly getting stronger and much more spirited shall we say. His 1 to 1 teacher made a statement which describes how he needs constant attention for this reason and how they are supposed to be doing more community based work with him but cant as he refuses to walk,sits down, wants to touch passing cars and attempts to step into the road. In school he swipes and throws things off the desk. He also constantly wants to chew his fingers and has to be physically as well as verbally stopped from doing so. At home   His doctor has put a letter just recently to support this so I'm hoping it will help. Just wondered if anyone else is or has been in a similar situation and can offer any advise? Thank you for reading.