Hello Panzee, I can't answer for ADHD I'm afraid but my son is autistic and gets DLA.
In one instance we discovered that at a certain time he was absolutely primed to begin signing and subsequently talking. Obviously the entire family had been desperately trying to encourage this but because his social skills were impaired he wasn't at that time ready to engage with us.
He was, however, starting to take notice of Mr Tumble / Justin Fletcher on television. We bought every available DVD from the Makaton website along with the Makaton handbook with the DLA one month.
My son has terrible problems walking around outside due to anxieties and phobias or cars, noise, crowds, dogs, you name it. We don't actually receive the mobility aspect of DLA but we used what we get for his care needs to buy a pushchair that I had never expected to have to buy for a child as old as he is.
But it is a godsend. The hood comes all the way down to shut out the distressing outside things, he can't drag his feet and ruin his shoes (another expense) and prevent me moving him anywhere.
My son has sensory issues and at one point I used DLA for a swimming-only membership at a health club. No overwhelming chlorine smells, a quiet, small, safe environment, walk-in pool and most importantly a playpen in the changing rooms so I didn't have to worry about him running back to the pool and falling in.
Luckily DS is not that violent or uncontrollable but I should imagine some parents of children with ADHD have to replace common-place things very often. Not just their own things, but those of their parents and siblings.
We go through bedsheets, duvets, covers and mattresses like you wouldn't believe due to incontinence issues.
Mainly I would say that DLA helps a child with ADHD in that it enables them to have a parent at home especially in the early years, who is available to sort all these things out and more importantly to fight for the provision that the child needs. I'm an ex-teacher and well-used to filling in complicated forms but I do get overwhelmed at the amount of paperwork I am asked to complete.
In addition, my calendar is full of meetings with various professionals. I can't see how I could get back to work at this stage even if specific childcare were available.
If the parent of a child with ASD / ADHD is on their own and has no respite at all, no sleep, then it's preferable that the family has a little bit of extra money to the child going into care with all the well-known outcomes that entails.