Appeal re child DLA + eligibility for enhanced mobility component?

The child is 9 years old. There is a diagnosis of ADHD +0DD.
There is no experience of ASD or SMI.
The current award is ERDL and SRM.
Mother is strongly of the view that he is entitled to high rate mobility.
This is partially because a sibling [who experiences SMI] has this award.

Understandably, as the parents see little difference is the supervision/care needs, they cannot understand why the decision is not straightforward.

Has anyone dealt with an appeal like this and have advice on how to present? case law etc?
It seems that the only option is to argue the child is frequently ‘virtually unable to walk’ by virtue of much higher supervision need [ which primarily speaks to ADL descriptors but could be given a mobility focus perhaps] and being overwhelmed by distress and therefore not consciously/wilfully refusing to walk.

Hi. I think although Autism/Autistic Spectrum Disorder has been accepted as physical disorders of brain development, would the same apply to ADHD? Without that, I don’t think the child will meet the criteria under virtually unable to walk that the refusal to walk (etc.) comes from a physical cause.
I found this page a helpful summary/reminder:
https://contact.org.uk/help-for-families/information-advice-services/benefits-financial-help/benefits-and-tax-credits/disability-living-allowance/claiming-dla-higher-rate-mobility/