DLA Change Of Circumstances

Hi all, I have a 5 year old nearly 6 years old son who is awaiting his Autism diagnosis. He already gets Higher rate care DLA and low rate mobility. I have more evidence from his physiotherapist and paediatrician to say that he needs 1-1 supervision from an adult at all times due to him having no awareness of danger. Basically my son becomes that distressed when we go outside due to his difficulties he will lash out at others, including punching, pinching, smacking and he will bite himself and others too. We have tried getting a big enough park that he will fit in but he totally refuses which leads to more meltdowns. Also he will go onto a road if a car was coming past and we have to physically restrain him all the time. if he was left alone for a second I would hate to think what could happen. We stay in most of the time with him as he is at his happiest. He is currently being home schooled due to the lack of support school we’re given ( basically school didn’t accept his needs even tho I had all the evidence but they still took off all his sensory support etc even though he was on the SEN register) we are complaining about this to the chair of governors and we are awaiting a tribunal for an EHC assessment to be done. I just need help filling in the Change Of Circumstances form if we are going for the higher rate mobility, any advice or help will be very much appreciated. Thanks