I get HRC and LRM or my 7 year old ASD son.
I made sure I listed all aspects of his night care AND how this was not normal for a child his age ..
example - My son wets the bed and needs changing regularly, I explained that most 7 year olds will go the toilet themselves.
Sounds obvious I know but not all the DLA staff have children and understand what a child could and couldn't do.
I would re-apply for the HRC and list everything you do in the night, keep a diary with dates and times, this will support your case massively.
We have door alarms for my son's bedroom as he gets up and wanders and I listed this, we have to wake up every time the alarm goes off and return him to bed, wait for him to fall asleep and re-set the alarm.
Again I listed that most 7 year old's sleep through the night and upon waking can be trusted to return themselves to bed safely and go back to sleep.
I really suggest you read Cerebra's guide to claiming DLA, it is fantastic for autistic kids and really helps make sure you cover everything.
Definately fight it as if he has night needs you are entitled to it!
PM me if you want any help or advice, I'm a bit of a DLA expert now lol although it took me many re-considerations and claims to get there.